I've mentioned this before, but if the goal is close access to magma and fast FPS, there's two options that have worked well for me.
The first is to generate a very thin world without any volcanism at all, and a single cavern layer. With that, (and there are examples in the worldgen cookbook threads in all versions that I should have done) you can get magma access within 20Z of the surface. Now, yes, it might require that you dig past the cavern layer without exposing it for FPS reasons, but it can be done.
Second way is to remove caverns entirely, and give your dwarves the surface farming trait. That way, you can have magma in less than 10Z away.
However, unless you're embarking on the surface volcano 1x1 tile, it will always be at least 20 walking tiles away from your embark location. My point? You can dig down to it and it will be closer by doing so than on the surface.
At least, initially.
As far as keeping FPS overall fast, keep your civs to under 10, and your sites to under 5, and your world size 17x17 (pocket) with the above in mind, and FPS should not be a problem.
EDIT: An example of what I mean...
14Z from embark to magma forges
One cavern layer, most subterranean trees
All races as neighbors (elf, dwarf, goblin, human)
Steel Friendly Embark (coal, flux, three types of iron bearing ore)
Flat Embark
Sand, Clay, Surface Water, Cave Water
No Aquifer
Hemp for cloth & paper
1000 year history (abundant and accomplished poets, musicians, instrument players)
populationsCivilized World Population
233 Dwarves
220 Humans
147 Elves
21430 Goblins
Total: 22030
worldgen[WORLD_GEN]
[TITLE:FAST_N_FLAT]
[SEED:ci4My6u4sAWiu6C4yU8S]
[HISTORY_SEED:MemewUGQcSCmwYY4ygMA]
[NAME_SEED:Qy0k8KiAsMMCk8EmMIaE]
[CREATURE_SEED:SIQsc44iWmcYI6siseK8]
[DIM:17:17]
[EMBARK_POINTS:2500]
[END_YEAR:1000]
[BEAST_END_YEAR:1000:-1]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:100:400:0:0]
[RAINFALL:49:75:100:100]
[TEMPERATURE:75:75:0:0]
[DRAINAGE:33:75:100:100]
[VOLCANISM:0:0:0:0]
[SAVAGERY:0:0:0:0]
[ELEVATION_FREQUENCY:2:9:0:0:0:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[POLE:NONE]
[MINERAL_SCARCITY:500]
[MEGABEAST_CAP:0]
[SEMIMEGABEAST_CAP:0]
[TITAN_NUMBER:0]
[TITAN_ATTACK_TRIGGER:0:0:0]
[DEMON_NUMBER:3]
[NIGHT_TROLL_NUMBER:0]
[BOGEYMAN_NUMBER:0]
[VAMPIRE_NUMBER:0]
[WEREBEAST_NUMBER:0]
[SECRET_NUMBER:0]
[REGIONAL_INTERACTION_NUMBER:0]
[DISTURBANCE_INTERACTION_NUMBER:0]
[EVIL_CLOUD_NUMBER:0]
[EVIL_RAIN_NUMBER:0]
[GENERATE_DIVINE_MATERIALS:0]
[GOOD_SQ_COUNTS:0:0:0]
[EVIL_SQ_COUNTS:0:0:0]
[PEAK_NUMBER_MIN:0]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:0]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:1000]
[RIVER_MINS:0:0]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:0]
[SUBREGION_MAX:5000]
[CAVERN_LAYER_COUNT:1]
[CAVERN_LAYER_OPENNESS_MIN:1]
[CAVERN_LAYER_OPENNESS_MAX:1]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:0]
[CAVERN_LAYER_WATER_MIN:52]
[CAVERN_LAYER_WATER_MAX:52]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:10]
[LEVELS_ABOVE_LAYER_1:6]
[LEVELS_ABOVE_LAYER_2:2]
[LEVELS_ABOVE_LAYER_3:2]
[LEVELS_ABOVE_LAYER_4:2]
[LEVELS_ABOVE_LAYER_5:3]
[LEVELS_AT_BOTTOM:2]
[CAVE_MIN_SIZE:1]
[CAVE_MAX_SIZE:1]
[MOUNTAIN_CAVE_MIN:0]
[NON_MOUNTAIN_CAVE_MIN:0]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:9]
[TOTAL_CIV_POPULATION:2000]
[SITE_CAP:4]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:0:0:0]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]
embark locationprospect[DFHack]# prospect hell
Base materials:
SOIL : 25131
STONE : 122593
FEATURE : 8646
MINERAL : 58307
MAGMA : 40248
ROOT : 1700
TREE : 4034
MUSHROOM : 1507
Liquids:
WATER : 2723 Z: 129..140
MAGMA : 33529 Z: 121..125
Layer materials:
SILTY_CLAY : 4980 Z: 140
LOAMY_SAND : 6327 Z: 140
SANDY_CLAY : 5783 Z: 139
SAND_TAN : 8041 Z: 139
SILTSTONE : 14651 Z: 136..138
CHERT : 18249 Z: 135..138
GNEISS : 15543 Z: 129..134
MARBLE : 31133 Z: 123..135
GABBRO : 19681 Z: 121..132
GRANITE : 20096 Z: 123..127
SLATE : 3240 Z: 121..122
SLADE : 8090 Z: 114..116
>>> TOTAL = 155814
Ores:
TETRAHEDRITE : 6157 Z: 123..135
MAGNETITE : 3711 Z: 136..138
NATIVE_SILVER : 2546 Z: 123..127
HEMATITE : 1806 Z: 136..138
LIMONITE : 1541 Z: 136..138
MALACHITE : 1483 Z: 133..135
RAW_ADAMANTINE : 556 Z: 119..125
GARNIERITE : 265 Z: 121..122
GALENA : 233 Z: 121..122
NATIVE_PLATINUM : 50 Z: 136..138
NATIVE_GOLD : 44 Z: 135..137
CASSITERITE : 39 Z: 136..138
>>> TOTAL = 18431
Gems:
CRYSTAL_ROCK : 211 Z: 128..138
MORION : 164 Z: 128..134
YELLOW ZIRCON : 159 Z: 123..134
GOLD OPAL : 155 Z: 123..127
PRASE : 135 Z: 123..138
AMETHYST : 135 Z: 128..132
ALMANDINE : 128 Z: 128..135
PIPE OPAL : 124 Z: 124..128
TANZANITE : 124 Z: 128..134
GOSHENITE : 114 Z: 124..135
SARD : 101 Z: 135..138
QUARTZ_ROSE : 90 Z: 121..134
SUNSTONE : 89 Z: 129..134
TIGER IRON : 87 Z: 136..138
ONYX : 81 Z: 136..138
SARDONYX : 80 Z: 136..138
SCHORL : 76 Z: 123..133
GRAY CHALCEDONY : 69 Z: 135..138
TSAVORITE : 66 Z: 133..135
GREEN ZIRCON : 64 Z: 133..135
PYRITE : 63 Z: 123..134
BONE OPAL : 60 Z: 136..138
BLACK ZIRCON : 57 Z: 121..135
OPAL_LEVIN : 57 Z: 129..134
MELANITE : 56 Z: 133..135
CARNELIAN : 54 Z: 135..138
AVENTURINE : 54 Z: 136..138
ALEXANDRITE : 46 Z: 123..127
CLEAR ZIRCON : 43 Z: 121..135
INDIGO TOURMALINE : 42 Z: 133..135
TIGEREYE : 42 Z: 135..138
BROWN JASPER : 41 Z: 136..138
CITRINE : 38 Z: 125..135
PINEAPPLE OPAL : 33 Z: 124..127
CHRYSOBERYL : 33 Z: 123..128
PINK GARNET : 31 Z: 123..128
YELLOW SPESSARTINE : 31 Z: 129..134
AQUAMARINE : 31 Z: 134..135
SPINEL_RED : 25 Z: 121..122
OPAL_HARLEQUIN : 23 Z: 133..135
WHITE JADE : 22 Z: 135..138
HELIODOR : 21 Z: 133..135
MILK QUARTZ : 20 Z: 128..132
PERIDOT : 19 Z: 121..122
RED TOURMALINE : 19 Z: 129..134
BLUE GARNET : 14 Z: 129..133
WOOD OPAL : 14 Z: 137
BLACK PYROPE : 13 Z: 122
HONEY YELLOW BERYL : 8 Z: 133..134
VIOLET SPESSARTINE : 6 Z: 122
SMOKY QUARTZ : 5 Z: 121..122
PICTURE JASPER : 4 Z: 135
>>> TOTAL = 3277
Other vein stone:
MICROCLINE : 11409 Z: 128..133
ORTHOCLASE : 7860 Z: 121..134
MICA : 7173 Z: 133..135
COBALTITE : 4717 Z: 121..132
GYPSUM : 1971 Z: 137..138
JET : 1957 Z: 136..138
COAL_BITUMINOUS : 1924 Z: 135..138
PYROLUSITE : 42 Z: 123..127
ALABASTER : 36 Z: 137..138
HORNBLENDE : 26 Z: 123..127
PERICLASE : 22 Z: 124..128
PETRIFIED_WOOD : 10 Z: 137..138
KIMBERLITE : 8 Z: 121..122
>>> TOTAL = 37155
Shrubs:
MUSHROOM_HELMET_PLUMP : 74 Z: 129..133
POD_SWEET : 71 Z: 129..132
MUSHROOM_CUP_DIMPLE : 71 Z: 129..132
QUINOA : 40 Z: 141
PURPLE_AMARANTH : 40 Z: 141
WEED_RAT : 40 Z: 141
BITTER_VETCH : 38 Z: 141
ROOT_HIDE : 38 Z: 141
SPINACH : 36 Z: 141
GRAPE : 36 Z: 141
KANIWA : 34 Z: 141
ASPARAGUS : 33 Z: 141
WILD_CARROT : 33 Z: 141
ONION : 32 Z: 141
HEMP : 31 Z: 141
BLUEBERRY : 31 Z: 141
TURNIP : 30 Z: 141
CHICORY : 29 Z: 141
MUSKMELON : 28 Z: 141
GARDEN_CRESS : 27 Z: 141
LENTIL : 27 Z: 141
CRANBERRY : 26 Z: 141
BERRIES_FISHER : 23 Z: 141
BROAD_BEAN : 22 Z: 141
SOYBEAN : 22 Z: 141
REED_ROPE : 21 Z: 141
>>> TOTAL = 933
Wood in trees:
WILLOW : 91 Z: 141
FUNGIWOOD : 42 Z: 129..132
GOBLIN_CAP : 40 Z: 129..133
SPORE_TREE : 37 Z: 129..132
NETHER_CAP : 36 Z: 129..132
ALMOND : 35 Z: 141
TOWER_CAP : 35 Z: 129..132
BAYBERRY : 32 Z: 141
PERSIMMON : 32 Z: 141
BLOOD_THORN : 32 Z: 129..132
APPLE : 31 Z: 141
GINKGO : 31 Z: 141
SAND_PEAR : 31 Z: 141
CHERRY : 25 Z: 141
PEACH : 25 Z: 141
BIRCH : 25 Z: 141
>>> TOTAL = 580
Has HFS tubes : 5 Z: 119..120