They run this class out west with a spec pipe and it is pretty popular. Not sure on the specifics with the WKA rules though and how they achieve parity between engines. They can be made to be similar in speed pretty easily with weight, exhaust, and clutch spec.
Depends on what clutch setup you run, but a Yamaha can with a clutch that comes in around 9k will almost always trump a KPV with a clutch that comes in at 5k off the corner. But the KPV will start to run away at the top end.
But again, depends on what WKA has for specs on the two engines.