But the only internal upgrades I know about, is the Teflon tape upgrade, and installing a tightbore barrel. There soon will be a reinforced bolt, I have heard, but I'm not holding my breath for it. The telfon tape upgrade, and the tightbore upgrade, are not easy to do, you should prior experience working with airsoft guns and small parts before attempting this, as for you will probably mess up your gun.
I Teflon mod my gun before everygame and on Op-Doc's crono I was doing 345 FPS with a .3g bb, but in all honesty I hear .23g is the way to go with these rifles. They are a fair shot and if you get the hop up just right you can expect to make a clean shot at 50 yards or more. Mine has a custom tape job as well as ghillie flauged which allows for people to get really close to me without seeing me so I usually take my shots at roughly 25 yards and I usually never miss. Anything longer than that you take 1 shot to calculate for wind/distance and the next shot is usualy a money shot. That's just my $0.02.