I just genned a world with multiple large rivers. This means a high probability of many waterfalls, and a decent chance of a truly large one, although I haven't explored too thoroughly.
pic, scaled down so it would upload, most rivers still visible. it's broken, nevermind
[WORLD_GEN]
[TITLE:LARGE_VOLC_COLD_WET]
[SEED:1848729848]
[HISTORY_SEED:1771707042]
[NAME_SEED:3413331786]
[CREATURE_SEED:3905482882]
[DIM:257:257]
[EMBARK_POINTS:2000]
[END_YEAR:1050]
[BEAST_END_YEAR:450:-1]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:1:400:800:800]
[RAINFALL:0:100:400:400]
[TEMPERATURE:0:75:400:400]
[DRAINAGE:0:100:400:400]
[VOLCANISM:0:100:400:400]
[SAVAGERY:0:100:400:400]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[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]
[TITAN_NUMBER:100]
[TITAN_ATTACK_TRIGGER:80:0:10000]
[DEMON_NUMBER:50]
[GOOD_SQ_COUNTS:100:1000:2000]
[EVIL_SQ_COUNTS:100:1000:2000]
[PEAK_NUMBER_MIN:50]
[PARTIAL_OCEAN_EDGE_MIN:2]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:50]
[REGION_COUNTS:SWAMP:1032:7:6]
[REGION_COUNTS:DESERT:1032:7:6]
[REGION_COUNTS:FOREST:4128:13:12]
[REGION_COUNTS:MOUNTAINS:8256:9:9]
[REGION_COUNTS:OCEAN:8256:7:6]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:8256:13:12]
[REGION_COUNTS:HILLS:8256:13:12]
[EROSION_CYCLE_COUNT:250]
[RIVER_MINS:800:800]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[CAVERN_LAYER_COUNT:3]
[CAVERN_LAYER_OPENNESS_MIN:50]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:100]
[CAVERN_LAYER_WATER_MIN:5]
[CAVERN_LAYER_WATER_MAX:100]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:7]
[LEVELS_ABOVE_LAYER_2:3]
[LEVELS_ABOVE_LAYER_3:1]
[LEVELS_ABOVE_LAYER_4:1]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:2]
[CAVE_MIN_SIZE:5]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:35]
[MOUNTAIN_CAVE_MIN:150]
[NON_MOUNTAIN_CAVE_MIN:250]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:50]
[TOTAL_CIV_POPULATION:50000]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:8256:16512:8256]
[RAIN_RANGES:8256:16512:8256]
[DRAINAGE_RANGES:8256:16512:8256]
[SAVAGERY_RANGES:8256:16512:8256]
[VOLCANISM_RANGES:8256:16512:8256]
I've found at least 100+ sites with waterfalls, mostly 3-4 high, a few dozen with 5's and I've found many that had 6-*(10-11?) story cliffs, two with a waterfall on either side of the major river, noting that these are all junctions of two or more rivers and that the falls are from the smaller cascading down into the canyon of the larger, but that's still pretty Fun.
Also, with the caves' entrances being on elevated plateaus now, you can easily find them on the site finder.