I think your str/power strike and the weight of your weapon is the main thing, going against the weight of the enemy weapon (which I believe is more important than the enemies str/powerstrike). But I really don't know off hand...I just know that when I was using my elite scimitar that 2h's and polearm users were consistently stunning me, but if I was manually blocking other 1h's, I didn't have near the delay in priming my attack vs the 2h great swords.