Sounds nice, are you 100% sure your mother board supports 16GB of Ram ?? just because you opted to slide in those sticks, doesn't mean your motherboard fully accepts 16GB of Ram,, might try like 12 or 10 GB of Ram,, mine actually lagged more with 16GB of Ram than 12 GB of Ram,, till I changed upgraded to a motherboard that supports that much along with a new XFX 6850 Video Card, theres a XFX 6950 also, and I've got a Quadcore processor as well.  and I run windows 7 on a 64 bit system,,, don't know maybe some of these other guys have some ideas. When you get into a more populated area with lots of heavy scenery buildings, lotta A.I. traffic and havey clouds, and Animations all trying to load at the same time, it will impact performance a bit too,,, so be aware of that also.  also don't forget to Defrag your system every once in a while too, helps speed things up, a tad bit too.

Try and use some of the tweaks in the tweaks section,they may help a bit...

PS:What's your traffic settings?since those are major FPS killers.

FSX was a badly coded setup to start with, and that still haunts users today.

It does not matter how much hardware you throw at FSX, running everything at max will never give a respectable performance.

One will have to set the sliders within reason to ensure a smooth experience.

I cannot fly at anything less then 20fps, mine is locked @ 30, mostly stay at 30 but at the expense of sacrifice.

I have 2 saved CFG's, one for commercial flying and one for GA flying.

In both those CFG's I have different settings, eg, GA flying I would have dense scenery & normal autogen where commercial I would have normal scenery and sparse autogen.

50% airliner traffic and 10 GA traffic on commercial where GA would be 50% GA traffic and 10 commercial.

Weather settings I kept at medium and one slider up for distance.

Avoid cars, boats and ships, they kill FPS.

Also use Nvidia inspector. This helps alot:

http://www.simforums.com/forums/settings-for-new-drivers-updated-v1959_topic3658...

Goodluck.

Had similar problems, did a reinstall onto SSD and most of the probs have disapeared, but still slows to a crawl in congested areas. hopefully P3D will resolve these issues in the near future and provide a clear migration path.