After a request from The Helldragon, and after considering the matter, I've decided to boost the maximum avatar picture size. From now on, you'll be able to use pictures up to
96x96 pixels.
The new size, just like the former 64x64, is a multiple of the standard icon format (which is 32x32). This also matches the double of a normal AIM avatar, which is set at 48x48. This allows you to reuse existing pictures without having them stretch oddly. The maximum filesize will remain at 50 KB, which should be plenty enough for anything normal. If you really come up with something which weights more, you should consider compressing your picture somehow.
The default remains at 64x64, and the stock avatars will also stick to that size. They'd look too pixelated if they were enlarged. Of course, nothing stops you from going in your profile to change that size if you so wish!
If you have any question, feel free to ask.