odd... I get about 800-1000 shots out of my 4500PSI/70CUi tank! Im guessing my RT eats up a lot of extra air or you have a regulator set to a lower PSI then what Im running (the HPA tank is set to 850PSI and the A5 is stock regulated other then that)?

Anyway, like he said an HPA tank should be your first mod for the A5 no matter what. This goes double for anyone who shoots with an e-grip or RT on burst/full auto modes. Using C02 and running automatic is a good way to frost up your gun and kill your o-rings (not to mention freeze your fingers!). Just screwing around with c02 in my back yard I got my RT/cyclone lines to frost up and that was with a very limited stream of rounds being fires. A few seconds more and the bdy of my A5 god as cold as ice. Im sure any more and my o-rings would have been toast.

This NEVER happsn with compressed air. NEVER. HPA stays in it's gas form so there is no big temp difference like you get with a liquid turning into a gas (e.g. CO2).

AFTER you go with HPA, upgrade the barrel. I suggest (on the high end):
Palmer Brass (for accuracy)
Faltline (for distance and decent accuracy)
Apex (to shoot around corners or drop balls on people behind bunkers)

or if your budget is limited go with a J&J ceramic. The one piece is decent and will shoot most paint with decent distance/accuracy. The 2 piece is better, but for the same price you can get a non coated/unvented Palmer brass barrel (~45 bucks).

After that you can go onto other things like stocks, different hoppers and slings (i find that my 3 point sling really works wonders)

Cliffs notes:

Get these in this order:
HPA
Barrel (Palmer brass, Faltline, APEX, J&J ceramic)
whatever else you may require

__________________
'07 Proto Matrix Rail (all composite changed to aluminum)
Dye Ultra-Lite frame
Dye Throttle 70/45 HPA tank
Deadlywind Carbon-Fiber barrel w/ SS Freak insert kit
Halo-B V35 board, Rip-Drive, & Bone boost battery pack