What are  you looking for? Do you want a higher top speed, or more pull out of the hole?
you will lose one or the other with any swap. It is just like swapping differential gears on a car.
My boat had stock impeller, and I wanted more bite out of the hole so I got a swirl from Impros and lost about 2 mph off my top end, but it hops out and planes immediately now. Which is what I wanted it to do. I don't run my boat full speed as much as I am being towed around on a wakeboard, so I needed more bite, and less speed. 
If you want more speed, you will likely lose a little bite and take a little longer to plane.
I called Impros and asked for Dave. I told him what I wanted and he recommended an impeller, and I have been pleased as punch since :hurray: