Do not install in the default location, choose a separate, different folder.
Use this page to optimise basics of the config file.
http://www.venetubo.com/fsx.html
Use an external frame rate limiter (30 works well for most), not the internal one. The internal you should set to "unlimited", the external to 30. Some graohcis driver seem to already have that feature, but also are reported to work unreliable.
Do not use DX10 in the sim settings, it is not ripe and creates artifacts.
FSX is no true and native DX10 sim. Blooming light effects and shadows also are performance killers. Keep traffic sliders at low, if you face system lockups (like I did): switch ALL traffic (air, land, sea) to zero, this cured my problems. Street traffic in general and air traffic is a known hog on performance anyway.
Check this:
http://www.simforums.com/forums/fsx-and-nhancer-settings-for-new-drivers-updated_topic36586.html
What kind of flying do you prefer? VFR or IFR at higher altitudes? If the latter, not all environmental addons are needed, since you do not benefit from gbround scenery when flying at 30000. Improved weather textures, weather install software, and airport sceneries is what I prefer, doing medium and high altitude IFR exclusively. If you do VFR at low altiude, imrpved mesh and imporved landclass files might be interesting for you. But they have an effect on frames.
As always, FSX needs CPU power before GPU power or RAM.
I am not experienced with Phenom processors, but I read 2.4 GHz per core, that maybe indicates you need to be gentle on FSX' internal settings. Start low and push them up slowly as well. FSX is no multi-core optimised title, and mainly uses only 1 core, the others help in improving the system and background tasks. FSX needs fast CPU before anything else. Check temp to not exceed critical values.