3"-5" works, but I find the blade sharpness and ability to hold that edge is FAR more important. I have field dressed and butcher to package 8 deer. My brother in law many times that many. He and I were talking and agreed that we were tied of having to re-sharpen our knives 2 -3 times for each deer. We were both using classic deer knives by big name manufacturers. Then I found bladeforums and KF. I now have several dozen deer size knives that stay sharp thru whittling many hardwood walking sticks (and one deer). Good knives in BG42, D2, A2, stay sharp. I even have a CS in AUS8 that seems not to dull now matter how much I cut, hack, chop with it. Length and shape are important, but steel, heat treatment, and edge configuration are what really matters.
Oh, I do have a bunch of Infi and SR101 but haven't actually used them. I bet they will work too.
I did try a 6" + knife once for deer skinning. Do you know how hard it is to field sharpen a 440c blade at 64.5 RC w/o diamonds? Only used it once.
Ron Athay