LolActually there seems to be no rhyme or reason as to which gun Max uses at any given match. I actually think he throws the one with the trubore barrel in the mix still.
As for barrel holes, being fairly new to the open game, I've only shot my own which has no barrel holes. Based off what I've seen, however, is that it probably only matters if you're at the top levels of this sport and can feel or take advantage of little changes to the gun. The average guy is going to go out and finish somewhere behind the top guys anyhow. I would just leave it up to the builders recommendation at that point. EG does just fine with his V12 or V8 Tanfo.
Take Lesgar and Max for example, two different builders with two different philosophies on barrel holes, yet they are both always at the top of the results.