I have had mine over a year now and I got mine second-hand, I did have a problem with the reg. If the gun was left and not shot for 30 mins or more the first shot would be 50fps less than the next one. I think it is a common fault with the EV2 for the reg to go like this, I sent it back to AA and cost me £50 to get it fixed, now shoots like a dream....
I would like to clarify when I say a common problem. There are quite a few EV2's out there that never have a problem, the very few that do have a problem seem to be with the reg, but that's it, not seen or heard of any other 'common' problems with the EV2, they are absolute cracking rifles....
I fill to about 190 and refill at about 100, never noticed any sort of power curve, well, not since it got back from AA...