well i dont know what would be "best" but i'm gonna try and run 500oz-in on all 3 axis.. i think that 400 might be a little much on x and y.. the whole thing about it is that you want enough to move the mass, and start and stop and whatnot, but if you go too big you start running into resonance issues and having to get bigger drivers (current carrying ability) there has been a really good discussion of dampening resonance on here, do a search for it.. one person made something that followed the "rattler" design, a dampner thats used on the front of an engine and reports from him and others say that it was very effective... but you wont know for sure what your resonance issues will be till you get it all put together and try it...
if you want the "best performance possable" then you should really look into servos.. but this is just like what the mechanic said in mad max... speed is a question of money.... how fast do you want to go?
my cncfusion kit is listed as "out for delievery" on the ups site this morning.. so i'm all excited...
Grizzly X3, CNC Fusion Ballscrew kit, 3 500oz-in bipolar steppers, 3 203v Gecko's, Linear power supply from Hubbard CNC, Mach 3, BOBcad Pro Art V22, Rhino.