I can't vouch for the novarossi mill or the rb, but I can vouch for both the 12 and 15 cvrx, even though my .15 is the non pull version.
These 2 mills are great. My .12, after break in, was a dream. Once I set the needles and everything, I barely had to retune the engine. I just retuned it because of the massive temp drop since my last bash at the park. It's a durable mill. The .15 that I have now was just broken in this morning. All I can say is WOW, big difference in performance. Of course I am still babying it since it's still new, but a big difference in performance. BTW, they both went into an NTC3.
The only difference in the .12 and .15 CVR-X is torque and hp. They are both relatively easy to tune and maintain. I would recomend them both. It's all about preference, not hp & torque. Ask yourself where you will driving your car ... bashing or actual racing. Myself, I mainly do parkinglot or schoolyard bashing with my brother or even just by myself. That being the case, I didn't see a real reason to get an engine with more ports and other stuff.
BTW, both the 12 and 15 are screamers! I love both of these mills.
