Markoz wrote on Jan 24^th, 2012 at 2:06pm:

Hi vans. I get nearly the same performance with Preview DirectX 10 on or off (down about 1-2 FPS if it's on) and seeing as I fly quite a few 3rd party add-on aircraft that are not DX10 capable I find it is better to leave it off. Other than that, I agree with you that Preview DirectX 10 is very nice. Mark

There is a nice little piece of software called Addon Converter X which makes almost all non-native FSX addon aircraft textures work in DX 10.
It's not free, $19.95 US, but if you like DX10, as I do, worth it.
http://www.flightsimtools.com/adconvx/
Regards,
Nick.