air use will go up with higher velocities, but sites will check the speed before you play so if you are playing at a proper paintball site get it to about 270 / 280 and leave it there.
If you're messing about on private land firstly be very careful, if the public can wander in you could end up with a big personal injury claim and or armed response unit if one sees you / gets hit.
If it is private games on land with permission please don't go over 300 fps - there's a couple of very good reasons for this, the first is the legal position, while the classification of paintball markers is a little bit of a grey area taking one over about 330 fps could be construed as a firearm resulting in a minimum prison sentance if found in possesion of it.
The other is that part of the reason that 300 fps was reached as a good speed for a maximum was that higher could result in broken little fingers if shot close up.
