If it's alum then is it safe to assume it's one of those small removable tanks like paintball use, like a mini scuba tank? If so then they should be cheap and you could just replace them if you felt the need, plus they can be pressure tested to give you an idea of their condition. I personally wouldn't worry about that pressure diff, but people rarely consider me a safe type. For example I always filled my Mrod to 3200 vs the 2900 max. Fyi I once had an 1800psi alum scuba tank that I had filled by a dive shop, when I connected the reg it read 3k! Now that concerned me and I released some pressure... My only real fear was dropping it like that. I assumed it would be ok if it didn't see abuse but Murphy's law dictates that would be the tank to have some bizarre accident and blow. Steel tanks I don't worry about nearly as much, carbon fiber or other misc wrapped tanks I fear above all but may be irrational.
I would work on getting the thing dialed in to max efficiency, like a hammer debouncer which gave my Mrod a LOT of extra shots. That gun also had the option of an extended tank which I had as well, so maybe they have one for yours? Or if an alum threaded mini scuba tank tehn maybe a larger one is available? I'm diggin the new Hatsan with two tanks, which I'm glad they did but wonder why it took so long? They also have mini CF tanks now, so a 4500tank with a reg would be the ultimate!? Imagine a nice fat CF of say 400cc regged to 2500. Yum...
Maybe rsterne has one, or can chime in on the possibilities and shot count?
rsterne: Every time I see your name I can't help but think of this in Heavy Metal:
http://tinyurl.com/o3xolej Great scene!