Best use a 1J spring to be safe for places where it's 330 or less. Really the 20 FPS difference doesn't make too much difference in such short areas like that and I calculated it once and there was only a hundreth of a second difference in striking time between a gun shooting 349 FPS and one shooting just under 1J (330 on .20's) hell I did it for 290 FPS as well and found it was still a negligible difference which makes sense if you think about it.
Basically to do this yourself consider Gr 11 physics and use the v=dt formula and isolate what you want to solve for and you'll see that a 1J spring (if not less as to decrease the stress and increase the longevity of the gun) is the way to go for CQB. You have v (your velocity), and d is assumed to be like 30 feet hallways or w/e (you can use any number you want) and then just solve for t.
That's just a suggestion though. If you want 350 FPS for indoor and outdoor play then that's probably a good way to go as well since it seems like you realize that the "magical" number of 400 FPS for outdoor play is not needed and that just being smarter and more crafty will yield better results than having the "best" gun on the field.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE