As long as your ball/bore combination is happy with a .015 patch, I'm confident that the little extra cloth for the .58 VS .54 will not make any accuracy difference you will notice.
At least in my experience, some of my home made pre-cut patches are a bit small, others are bigger and I have to tuck them into the barrel before ramming. Extra patch material has never made the slightest difference in accuracy that I have noticed. Im sure that if you went to an extreme with patch cloth volume, it would be noticable, but what you are talking about I personally would not worry about.
(stay tuned though, sombody could show up and blow me out of the water) :results:
Good Luck, Jeff