You should call Wes at Ultra and ask him. He just built a 900-1000 hp pickelfork recently and went down that same road... http://free.***boat.net/ubb/biggrin.gif
J/K Andy. I would go with a detailed Berk "A" impeller for starters. See how it runs, and start playing with other stuff down the road. A used "B" cut aluminum will cost around $100-$200 depending on the quality and style of the cut, as well as the condition of the impeller. A stainless impeller is the deal, as far as out of the box performance goes. They run around $800 and are a bolt on improvement to a stock impeller, but comparable to a well detailed stocker. Cutting them is a bitch though.
If you want, I am doing a comparison test between A's and B's in OTR. I will swap you my A for your B if you want. That will help me with my testing. Save me from cutting the "A" and help you out. I plan on staying with the "A", but I am going to try a "B" just to quiet some theories running around about a mph increase by cutting the impeller.