You can of course down load the BFD3 demo if you haven't already.
It's on the BFD3 info page on the right hand side.
It does, "as you would expect" have some major limitations with regards to velocity layers, 16bit and very much reduced articulations on snare and hi-hat in particular but it still gives you a good idea of the power of it's features.
I haven't bought any expansion since using BFD3 but since I already had quite a few as well as BFD2 I'm pretty good for a while.
As for Superior Drummer 3, one of the Toontrack guys was on the KVR forum last year saying there were no plans whatsoever for a Superior Drummer 3 which I found very baffling.
I'll see if I can find the thread
Steve