someone proposed dfhack fastdwarf to speed up construction with fewer dwarfs and low fps. Don't. It kills your fps and when it reaches 2, 1 or 0, your game is likely to crash.
repeated: turn temperature off. No you won't be able to unfreeze water with magma now and creatures won't die in it. Magma forges still work though. However, it will save you a load of fps. magma dumping is also fps draining because the game is now tracking burning/melting items. If they were metals, metalic globs will remain, wood might leave ash, etc. With temperature off, atom smashing is the only solution.
the pop cap works very simple. People call it bugged because they don't understand how it works. The outpost liaison/caravan reports how many dwarfs you have. If it's below the pop-cap, you get 3 more waves based on wealth. So yes, insane amount of rock or gold crafts just to trade with the caravan for stuff you might not really need yet can cause a lot of migrants to show up. Trading a few mechanisms for booze and an anvil (if you didn't bring one) and just making some wooden cage traps against early thieves and ambushers, and even the next few waves will rarely push you above 70. With my pop-cap at 55 I never get more than 5 waves, unless I get massacred along the way.
If you're using the pop cap, use the child cap as well. One number there is an absolute number of the maximum amount of children, the other as a % of the adult population. default is set at I think 100:1000, either stop at 100 or 1000% (10x) adult population. A bit impractical. What I currently use: I don't want more than a third to be children and never more than 25, so 25:50 (the 50% is a third of total population, half of adult). If a lot of adults die, I could change it.
@masterwork: one change is removing lots of "special" names, so for example leather is leather instead of turkey, dog and cat leather, which is easier on your processor. A small note however when you have questions, tell people you play masterwork mod or you might get confusing or confused answers.