I have no working knowledge of PCPs at all but I could understand an unreg'd gun through it's sweet pressure range being more consistent than a reg'd gun IF the reg'd guns regs are not totally consistent. I.e. Would expect cylinder pressure to fall gradually as gas is used during shooting, so fairly consistent between shots, where-as if a reg filled some chamber to 105bar on some shots and 115 bar on other shots the unreg'd gun might be more consistent during (say) a set of 5 shots.