In my opinion the 5.5 will be the better balanced length. You will also get another 50 to 60 fps higher velocity with the same ammunition as well.

I like the 5.5 inch barrel on my Blackhawk to me it looks and feels right. performance wise there will not be much difference. Get what "looks" right to you and be happy

You are really not going to notice much difference with 3/4 of an inch in barrel length. If you are going to carry it a lot get the shorter barrel.

The 5.5 will be more accurate at longer distances and yield more velocity. Go with the 4.75 for close range.