If you've abstracted the interface for it already... you might as well switch to 2.0 now and get the performance boost. If it turns out to be unstable, then you can just switch back to 1.x
I agree usually when they hit RC they are pretty much stable except for maybe some rare case bugs. So there is no point is waiting in my opinion. I was using SFML 2.0 while it was a RC for a long time and never ran into any problems.
Release candidates usually are basically the release version in its trial run. If no major bugs arise that they can't fix during that trial run and if the dev's don't decide they want more features added to that version it will be upgraded to full release after a while (Varies on how long).
Plain and simple its the final beta test they do to get testing with the masses after they have already done multiple other beta tests (Usually closed but it can be open also) and intensive internal testing.
Chrisname is right your game might be running fast right now but what is to say you won't have problems later when you have multiple levels and hundreds of textures and other resources? Might as well port it while it is smaller then porting it while it is larger.