I wish there was a demo of DX10 fixer. I was all excited about it until I saw the price tag. $30 is too much to experiment with.
My experience using it on two different systems was it did nothing for my performance. Certainly if you're running DX9 on a decent system and follow Kosta's guide then DX10 is no better or worse. If you do switch to DX10 be careful with some of the DX10 guides, particularly the one on Avsim which has some very strange ideas, and tells you to do some stuff that's just plain wrong.
Where DX10
may make a difference is more efficient use of your 32bit VAS, so if you are running FSX packed out with all sorts of addons you have a bit more headroom before you hit the VAS limit and get an OOM.
