As long as the crank pulley is the same diameter as the water pump pulley you're ok. If the water pump pulley is smaller than the crank pulley that's great. Depending on your rpm and what water pump you have, up to 20% over driven is great.
Under no circumstances should the water pump pulley be bigger than the crank pulley, with one exception. If the rpm is high enough you can run into cavitation and that's bad. If you contact Flowkooler or Milodon they can tell you at what rpm the pump will cavitate.
Then it's simple math to figure out how fast the pump is turning. If your max engine speed is say, 8000 rpm and the pump is 20% overdriven the pump rpm will be 9600. That's an example and I have no idea what your max rpm is or how many rpm the water pump can turn.
One other thing to remember about water pump speed. You can get to the point where you blow the belt off. This is much easier with a V belt arrangement but a serpentine belt will come off if you over speed it far enough. Also, I know you don't run a mechanical fan but if you were you'd need to consider fan speed as well. An exploding fan is bad news.