Alright, assuming Kain is 6 feet tall and the reaver's blade is 4 feet long (assuming a fully extended straight armed single handed grip, when he obviously prefers to use both hands, and thus will have a smaller perimeter):
The radius of a full 360 degree swing would be 7 feet, and it's full perimeter would be 43.9 feet. Divide that by 2, for a 180, and we get a generous 21.9 feet travelled by the very trip of his sword.
Now, we multiple this by 2.8 to find out how far it would travel in a full second.
61.5 feet per second with berserk on, for the very tip of his sword.
Edit: How much better would you say Berserk 3 is, Astner? Also, not sure if Charm 3 would be effective or not. I know Spidey's been effected by things like that before, but he's also resisted them before.
The question is how powerful it needs to be to do the former.