when it comes to going big i know what you mean, but when it comes to going big it costs money. if youre worried about having to buy new pipes for the xcr top end, well youre gonna have to buy new pipes for any big bore. stock xcr pipes are a dime a dozen and work exceptionally well. it all depends what kind of money you really wanna spend. and what your really wanna achieve. if youre racing id say yes go bigger, if you trail ride and ditch bang my personal opinion is bigger isnt worth it. a properly set up 600 or 680 in the ultras case has plenty of performance, just put the money youd be wasting into a top end into clutching, suspension, etc and i feel youd be alot happier.
my opnion, and yes my experience. i put a ton of money into going bigger and yes its alot of fun, but if i had half the money i feel i wasted being young and dumb, id be paying cash for a new sled.
going bigger PROPERLY costs a ton more then rebuilding your ultra.