At XT our typical engagement range was 10-40ft back when I used to play
My UMP was 260fps reliably, and it was dead accurate and ranged the whole arena with .20s. Never had any problems with it. It even shot 200ft outdoors, just very slowly lol
FPS means nothing indoors, the extra quarter second it takes for a BB to travel 25 feet between 300 and 400fps is nothing. You can't spot and dodge BBs that fast
And no wind means no need for heavier ammo.
Outside is a whole other game, much different physics due to the addition of extreme ranges and wind.
I used to have noobs that thought a 50fps difference was huge indoors. You don't even feel a 50fps difference when it hits you, let alone in performance lol