That set up should fair pretty well for FSX.
for starters you should have your flight sim installed on the same hard drive as your OS, this holds true for both FS9 and FSX this will help performance some.
Also a good solid defrag directly after installing would be beneficial as well.
There are a few autogen tweaks that should help with your frame rates, but as in the past you will need to play with your settings to find the best medium of image quality and performance. Hard to give specific tips here as even computers with similar specs get a variety of results.
This one by far the greatest for me yet
http://blogs.technet.com/p-12c_pilot/archive/2006/10/10/Autogen-tweak-that-might...along with this one add this under the "main heading" in FSX.cfg
FIBER_FRAME_TIME_FRACTION=0.33
Check some of the posts here on this page for some minor tweaks you can try. These have help me a lot even though I was running pretty good right out of the box.