It has been my understanding that the best torque and HP is at or around 8150 rpm. Sounds like you are a bit high . .?
This is with the stock pipe/can. With the SLP Pipe/can it shifts the power band farther and makes peak HP around 8300-8400 RPM.
I had a chance to take my SLP piped AXYS out this last weekend and it definitely is running good. I ride between 0-3000' and was pulling around 8500-8600 RPM with MTX 74G base weight with 1g at the heel with a Team Lime green 150/340 spring. This was also in ethanol mode and no resistor in. I need to add at least 1G to the tip and see what that does. Overall I am pleased on how it runs. My engagement is slightly high at 4300 RPM. I may try a lower initial rate spring, like a 120/340 or throw more weight at the heel to get back to ~4000 RPM engagement.
No signs of belt slip in the primary or secondary either.
I only had a couple little burbles or hick-ups when stabbing the throttle from a dead stop. I think it was over-revving, although the AXYS doesn't respond the same way as a Pro motor when it over-revs and throw a det code.