I prefer knives that are around 7 1/2 - 8 inches overall. At that size it is very easy to control and I have a good feel of the knife. Within reason, it is more about the person doing the work, than it is the size of the knife imo. A 4 inch blade used correctly, will do everything that needs to be done on deer, elk, and bear... YMMV
A bigger blade does not mean that the task will be done faster because of the extra size. But then again, I'm very fussy about how my game is taken care of,
so I don't always do it as fast as others. But the end result is much cleaner IMHO.