The cylinder won't affect efficiency
Assuming you have a standard 48ci 3000psi cylinder you would usually expect 500+ shots
http://www.scubatoys.com/paintball/paintballshots.asp
Look into efficiency of your gun. For starters what gun, what velocity are you chroning at, how well does paint match you barrel, when was you gun last cleaned & lubed?
What you can do is buy a bigger cylinder, and only if you can get 4500psi fills then you can take advantage of a fibre cylinder
However that will come at expense at around £150
If you can't get 4500psi fills at the site and can't improve efficiency then its cheaper to buy another 3000psi cylinder and carry a spare to switch