I remeber seeing that a 6.03 was the best of all worlds. a .01 is too tight, and anything bigger is bad.
This is the impression I'm under. Cheeseman is probably the most knowledgeable on this subject around here.I use a 6.01 on the untested theory that when/if the bb bounces around in the barrel it will give it less room to bounce around, and so will give it less room to exit at a diagonal. I could be completely wrong but it's just a theory.