Ok I checked out the new ones, with my pretty mid ageing computer, tested FPS on 4x4 standard embark, just after starting so not many dwarves, no caves etc. no flowing water on embark
Multithreading on: 20 FPS
Multithreadong off: 25 FPS sometimes dipping a bit lower but never below 20
World 2 I get about 25-30 with mutlithreading
World 3 HUGE improvement, around 40-45!
As for actual preference, I like world 1 the most, there are SOOOO many sites, which seems more exciting to me, I also like that there are a few disparate islands but people like me would definitely be in for a bit of a FPS slog, I'm fine with that (you should see how slow playing seamenace is), but there it is for other people to consider.
I also like world 2 more than world 3, it has a more spaced out feel, a lot of plains it seems to me, overall size apart world 3 seemed a bit sparse.
All that said maybe it's better not to be so ambitious for such a project

At any rate if we're making the decision based on FPS I think we should be going all the way down to world 3