Try Gaco's tweak. Post #60 on this page>
Works very well. I find it hard to believe DX9 is worse than DX10 for you. Try this tweak with DX9 and see how it goes.
It's very easy and you don't have to change any files. Just create a new text file called 'system.cfg', copy all the text from that tweak in to it. Then bung it in the Crysis install folder.