At this moment there is a huge performance difference between 32 and 64bit! But that doesnt only result of the 64bit feature which means that a future 32bit release might also get fast speeds...
I'd say an average of 10-15 FPS, some games more. They are working on a new 32 bit build and I see no reason it cannot be as good as a 64 bit version with a lot of hard work.