Hello Tim and Ron,
I am using DX10 exclusively. I used the patches from Steve's page with a lot of playing around and swapping between DX9 and DX10. Since the DX10fixer is out I stick to DX10. IMO it is a huge progress ! Of course it takes some time to configure your FSX but it's worth the effort. It is essential to follow Steve's notes concerning the Video inspector. In my case I'm using the NVidia inspector. Installing the Fixer is easy and configuration is straight forward. A look at the DX10 Avsim site is a must as you can find profiles for your graphics and some great hints. It's all about the time you want to invest.
Of course this is my personal opinion but I definitely recommend the jump to DX10. Couple it with SweetFX (freeware) and you have a new FSX.
I can't judge it compared to P3D2 as I never used latter. FPS ... to be honest I never look at as long as I'm fluid ;-)
brgds, Lex