Thanks Curtis. Hey CCurtis what is the stock bore of the 650? And 102mm is about it for punching it out right?

 

you can go 103mm. You should try to get around 260-270 psi for a screamer of a motor

 

Tony,
stock bore is 100mm- I went 103 and feel like it'll hold up just fine. I run my bike as hard if not harder than most and would go 103 again in a heart beat - it's up to you. I like to get the most bang for the buck - cost is sixes.
My compression with the 12:1 at sea level was 245 at 4500ft it's 215.
There are many factors which affect compression psi - including cam style , cam lobe center angle, velocity of intake etc...