Have you checked out some of the exhaust theory threads? If you can follow the math/science in them, they give you an idea of how I.D. and length of a pipe can add/take away power to a given RPM range.

So if you wanted to give a little more grunt to say the 3500 RPM range, you'd have an X length exhaust, but something at the 45000 RPM range would be a touch shorter.

Might be worth looking into. There is also the old saying that it is easy to cut something shorter if you find it is too long than to add more if you find it is too short.