Avatar size requirements (not file size) aren't just there for 56K users. If that were the case, we'd have smaller ads and such.
Part of the reason is avatars above the file size limit either break the tables or make posts that should be smaller into larger posts that have a lot of blank space. For example, compare your post to Crimm's. Both one liners, yet your post takes up about three times the size of his.
Now, let's make your avatar 50% bigger. How much bigger does your post get?