we have a similar setup to what you have mentioned. Its a 2010 rush 600 with a pipe mod and a gabes kit(p2) secondary geared down 1 toth on the top. it is getting stretched to a 137 at the moment. we had very little riding last year but it it appears we will have to add some more weight as it comes out at 8100 and quickly climbs to 8300. It is noticibaly better than stock but I think if it comes out at 7900 loading it hard and building heat fast in the pipe then get to 8100-8200 would be the best.