The advantages are several.
The port timing of the two bikes is different. The 200 being more aggressive, so if you go the big-bore route, you'll have that advantage still with you.
The 220 33mm carb is money waiting to be spent.
With the EG 225 kit, you get the choice of porting...bottom, top, moh-better everywhere. You wouldn't get that with a 220 of course.
My $.02, I'd prefer a Pro-x piston to a wiseco. Oh well.
***edit***
That's misleading. I understand that Pro-x doesn't make all (if any) of the pistons they have for the 200. Not according to their catalog anyway, and they haven't answered my emails to say otherwise. I just asked them again 'bout that. IF I had the choice, I'd prefer a Pro-x to a Wiseco. How's that?
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Kelvin didn't say particularly, but I'll bet his 225 waxes the 220 all the way 'round, too.
How come I don't have one, yet anyway.........that's what I wanna know!