Honestly I'd leave it alone.
If you're getting 540 at the crank and 450 to the contact patch that's a loss of 17% which really isn't that bad. Getting the losses down to 7.5% will I think be mechanically extremely difficult and expensive.
I hope the speed shop wasn't more interested in your $1000 over the correct spud. If you went with a Demon, assumed you've got 85% volumetric efficiency and spun it 6500 then you'd need a 720-750. A 950 will be letting in just a little too much when you drop the hammer.
A little pricey but VCP
http://www.verycoolparts.com/Stack.htm could be 1 way to recover a few ponies and give you a lightbulb throttle response.