I found the 756 rear to hook up well for a while, but the knobs round off very quickly compared to s12's. The main reason I won't be getting another 756 rear is that they don't inspire any confidence in fast flat corners. They seem to hook up well until push comes to shove, then they will slide out very suddenly and unpredictably on any given surface. I think an s12 rear will slide out sooner, but much more predictably, ie the s12 is a better rear tire imo.
The 756 is great front tire. It does well on all surfaces, unlike the 755 front which I found good in sand, very poor in mud, and no better than avergae anywhere else. Pirelli's MT44 is a very good all round front tire too, and wears better than the dunlops.