Crysis demo DX9 vs DX10 Performance
 

We were told Crysis would perform better in Vista but this apparently excluded DX10 performance as both the 8800 GTX and Radeon HD 2900XT were slower in Vista/DX10 when compared to XP/DX9. While the GeForce 8800 GTX only suffers from a small performance loss the Radeon HD 2900XT is completely killed off in Vista. Therefore I recommend anyone running a Radeon HD 2900XT either stick to XP or run in DX9 mode under Vista. Based on the CPU Scaling results it means that Crysis is not that processor intensive when you consider that a 1GHz drop in frequency only accounted for 2-4fps.

http://www.techspot.com/article/73-crysis-performance/

They did not compare DX10+Very High vs DX9+High, since it's the Very High setting which gives DX10 the "edge"...

The question is, are the two high settings comparable.