I have a blaster limited in an X2 with a fairly warm 780 kawi motor. I was able to get it in there with zero hammering on the chamber....but it was not easy. I had to do some massaging on the exhaust manifold for the chamber to clear, cut off the mounting bracket from the chamber, melt/massage the gas tank slightly, and cut out some of the baffles in the hood for clearance. Seems to run pretty well, but I suspect a superjet chamber would work just as well. It didn't look to me like the superjet chamber would work as easily with the stock tank.
If you can get the superjet chamber to work with the stock tank (probably will take some heating and massaging), or you're willing to use a different tank, the superjet chamber is probably the easier way to go and probably virtually the same performance.
I've heard that a superjet tank fits nicely with a superjet chamber, but have not tried it myself. Battery position could be an issue.
I also like the stock aluminum round nose superjet waterbox better than the stock X2 (or really any aftermarket X2 box that I'm aware of) but that is also not an easy drop in deal.
When you say "stock 650 chamber" do you mean the stock kawasaki "bone stock" exhaust, or do you mean the factory pipe 650 chamber? I would be very confident any of the factory pipe aftermarket pipes would be better than the bone stock exhaust, I'm not so sure that the waveblaser or superjet chambers are a big improvement over the factory pipe 650 chamber especially if it is a relatively mild motor package.