Well, that is a very nice game!
My FPS hovers around 55, although it once dropped down to 22, but that must have been a code error, because I didn`t notice any difference in the speed of the cube rotating.
Are you using a skybox, or just a plain object for your background?
It would be cool if you could rotate the skybox with the cube, to get a feeling of the surrounding, if you are using a skybox.
I am just guessing, but I think that when you rotate around cube, you actually rotate the cube, and don`t rotate the camera around the cube. If so, please make the cube static and rotate the camera. It makes it much easier to view.
Looking great!
TheComet
Peachy, and the Chaos of the Gems