Found this on the officials:
http://www.honorbound.se/Slamdps2.pdf
Its a rather lenghty theorycrafting on how slam can be used to improve dps.
it does, scales with str and shield block value, and crits quite a lot for 1k+ over here
I think you got the wrong slam there gorion, this guids on Slam, not Shield Slam.
ah, whoops
interesting stuff