Nokia 500 is running Symbian Anna out of the box, but its performance is quite disappointing. The reason is quite simple - there is no GPU in the Nokia 500 and its CPU is handling the GPU calculations instead.
We can't promise you the things will get better with the Belle update, but still - it should be worth updating. After all, how worse can it possibly get?
If you own a Nokia 500 you should be able to upgrade it with Belle right now by using Nokia Software Updater.
Thanks everyone for the tips!