Surestick: Once you A/S a tank you can use it on any markers, just drop a tank O-Ring in the ASA and it will still seal. If you shoot ropes, the valve won't be as open, so you can get shootdown similar to having too many or too slow regs on a HPA gun, a lack of air flow, not temperature problems. Someone may come in and tell me why I shouldn't do this, but it works damn well for me.
And I can get away with CO2 temperature wise, the coldest I have ever played in was about 70ºF
. If I ever move up Nord, I'll have reason to consider getting a 13/3k or 22/3k (hydroing sucks). As for cost, well, I find A/S and a $40 reg do more than enough (I only have a few markers anyways), although I did once do A/S, XChamber, and Reg, only because the regulator had bad seals, and the shrinking metals caused it to leak. The chamber was free, but I will admit, it made for a slightly bulky setup. One thing to factor into cost is that a regulator will last you 20 years and only need a few bucks worth of O-Rings and oil. A "normal" (not 13 or 22 ci) HPA tank will last you 10 years and cost more money in the form of hydrotesting.
I'm able to stay fairly objective on it all, I am not trying to prove anything by sticking to CO2 (although you would think so with the flames I recieve on Specops and whatnot), but really, at this point, I am fine. I am always shoppping for that HPA tank that will fit my bill, but so far, none have been the right one.