Are you using this for CQB? Because 390 is about perfect for outdoor (assuming 400 limit, note that I say limit and it's not a goal). .28's are great even though it'll bring the BB down to like 340-ish or whatever it'll fly straight and true (due to momentum and crosswinds don't affect it as much), also better energy retention for punching through leaves and light brush.
If you want a CQB gun "M90" is perfect. You really don't need any more because of the short distances and reaction times needed to even try to "dodge" a BB (do the calculations and even at 270 FPS vs 350 FPS indoors the BB's time to target isn't that much different at like 10-15 metres).
BTW depending on the gun the spring will wear out a bit and "settle", I know the "gen 1" APS guns had spring that shot 450 out of the box but would rapidly drop to like 370 or something after a bit of time with the spring compressed or through shooting it in your backyard/basement.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE