syntaxerrorsix; less fills? Or was that a typo? Generally pcp folks only buy the 4500psi tanks b/c a full 3kpsi scuba tank on a 3kpsi gun obviously can't bring the gun to 3k even once. If you spring for the 3440 tank then you get a few fills but still nothing compared to a 4500 tank.
Optionally people can get an elect pump. I just bought the Shoebox F10 which easily pumps past 4500. It's slower filling a gun that using a tank, a few min vs a few seconds, but you never have to deal with driving to the fill place, waiting, hydro etc. Hardcore peep buy a 4500 tank and the pump so they can fill it themselves. I have a nice 74CF carbon fiber tank but it's been expired for ~5yrs now. Tempting to fill myself, and prolly fine, but that's just too much pressure to risk it.
Another sweet deal w/ the carbon fiber or glass tanks is the weight. Mine only weighs 12lbs. A 3440 steel tank is a beast to take anywhere, especially since you get so few shots from it.
A friend uses two 3k alum scuba tanks so he and a friend(s) can drive out in the sticks to shoot. He over fills them to get three fills from one tank, then to squeeze out an extra couple fills between them he'd use one tank until it can only partially fill the gun, then the other tank only to top off the remainder. So the shooting day is always very short due to air, and a extra pita to do all that. A single carbon fiber would've gave him ~50 fills, much less hassle and no risk.
Fyi here's a fill calc if anyone wants to get an est of how many fills whatever tank will fill whatever gun:
https://sye.dk/airgun/index.php