I put a biturbo on my 08 sprint, and kept the jet's the same. Maybe 5mph top speed increase.
I put on a high flow intake as well, and upjetted from 55 to 58, but did not upjet my idle (which stock is 28) and i could hardly get the bike to run - it fourstroked like crazy.
Once I get the idle jet, i think the bike will be sweet and run great.
47steve - are you talking about the air mixture screw next to the idle screw?