The 2007 showed 1 more hp from top to bottom, and it does have a lot less of a "hit" than earlier models. It has several improvements to the carburetor , and uses the 450X sized intake valves, all of which make the bike very easy to ride,and yes, more horsepower.
By the way, Team Honda has been doing the 450X sized intake valve thing for a few years.
I have a friend from work who has been racing for years, and has changed the whole top end back to the 05-06
If he really did that he sure wasted a bunch of money. As mentioned, the only difference is the intake valves and porting, along with the carburetor.So, there's no "whole top end" to change, just the cyclinder head. All that to decrease the power .
The way a bike feels can be deceptive,that's why it'a good idea to do some homework before doing anything rash. Doug