You can get any gun to any FPS you want with a simple spring change. The question is whether it's going to break at that speed.
You'd probably want to get a reinforced gearbox and such.
At 450 FPS you're not going to be able to game an automatic gun. You'd wither need a BA (Bolt Action) or AEG pinned to single shot only (MOSFET is an option).
All of the guns are realistic, if you mean external materials then TM makes plastic bodied guns but they're "the best around", other than that there are a slew of companies that make metal bodied guns but you need to be AV'ed in order to get metal bodies, the best you can do with no AV status is 99% metal guns except for the receiver.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE