[Hectic]

Other way around. A bigger bore=more volume, so more volume wasted, so lighter ammo. Makes perfect sense if the barrel is wider it has a larger volume larger volume uses more air the to push the same bb, again as my math shows the impact is quite small goin from 6.01-6.05, but for arguments sake if a 6.01 performs great with a .30 the same gun with a 6.05 may run beter with .29 or .28bbs.
and 6.01 is good so long as you clean it regularly, 6.03 are also great and you dont have to clean as often. more importantly than the id is the consistancy of the bore. A high end 6.08 will out shoot a crappy 6.03 all day long.