If you still have that stock pipe use it for a boat anchor!! I have two 650rs and i put Pro Circuits on them both!!! The difference in the torque curve is felt as soon as you crack the throttle! I can wheelie in any gear any time. That is the best spent money you can spend to get where you want to be. What gearing is on your bike? I run stock US gearing. And as far as 450's go let's see i have not had one keep up with me on the street in the dirt or climbing hills. If you are big enough to ride it you can ride it anywhere fast. And I am still using the stock carb the edelbrock i had was a piece of crap! I got the stock one to work fine.