please do, i personally find it difficult to believe they would even bother to release a new DX version without there being some kind of significant change...and even more so...i find it difficult to believe that phong shading alone is causing you to drop 40fps, there is something else you are missing out on
EDIT:
this is what ive came across:
DX9
DX8
you seem to lose water quality in DX8, and that
does explain the frame loss when you switch to DX9, as water is a pain