Makeagif you can click on the advanced settings and put it at either 60x60 pixels (avatar)
or put it at 80x80 pixels (Signature)
Basic Gif Options
Switch to Advanced Options
Loop gif animation Yes
Animation speed Fast Medium Slow
Resize for AIM buddy icon Yes No
(My settings, fyi)
Advanced Animation Options> Custom widthxheight, (60x60)> Create GIF