I voted for just slight increase. Why clutter a text based forum with huge avatars?
I agree with this. Avatars are nice, but if they hinder the practical use of the forum in any way, then they are too big. Slightly bigger may be nice, but I do not see a reason to make these kind of things so big, that when someone posts a single line of text, the height of avatar and signature take up 7 inches on a 1080p 24 inch monitor like in some forums.
If they are allowed to be bigger, ideally there should be some user option to scale them back.