I have an A-5 and I run Air. When I would use Co2 it would freeze my gun but when I got my Crossfire 68/3000 tank it was so much better. If you are going to get a Compressed air tank I would get a Crossfire inc.
http://www.crossfireinc.com/products.asp?cat=10
When I got it it was $195 now it's on sale for $139. GREAT BUY