Exhaust+MCM+Lidless CVK setup gives you a whole "new" bike. Full exhaust if you want to max-out 6k-10.5k, stock header if you want to max 4k-7k power..
You can read/study about this for weeks in here..

 

The kustom Kraft kit is a bored 300 cylinder to 330cc and then replated. I have this kit. Yes it is thin but nobody seems to have issue.

Bill blue has a 331 kit or 351. He uses a Steel sleeve. Stronger then the factory aluminum cylinder and Kawasaki's whatever they call plating. Again no issues.

As for exhaust I like the fmf powerbomb with q4 slip on muffler. Louder but not stupid. Makes a big difference without the stock pea shooter.