Whats the difference between the 03-06 cylinder head and the 07+ cylinder head on the 600RR? I noticed they have different part numbers for the 06 vs 07 head gasket, which says "something" is different. However, when I compare pictures of the deck surface they look identical.

Any ideas? Whats the performance difference between the 06 and 07? Is it appreciable or "nehh"?