HD7850 + FSX optimization issues

Hey guys, it's been a while since I've played/flown FSX and I recently just build a new rig, though admittedly I picked parts out specifically for a different simulation, but I figured I should at least be able to play FSX on somewhat average settings, but apparently not.

Computer specs:

Windows 7

ASUS M5A97 motheboard

AMD Phenom 965BE 3.4GHz

HD7850 2GB

8GB DDR3 RAM

750W PSU

1280x1024 @ 60Hz

The sim I spend most of my time on, Falcon BMS 4.32, gets great framerates (45-60) with max settings, but of course the scenery is nothing close to FSX. I thought that with such good results I should at least get a decent framerate with scenery and autogen on dense. I added this line to the FSX.cfg file, as I did back when I used my dad's old computer:

TERRAIN_MAX_AUTOGEN_TREES_PER_CELL=800

TERRAIN_MAX_AUTOGEN_BUILDINGS_PER_CELL=800

Didn't really do anything. With aircraft settings at high or ultra high, scenery and autogen at dense, I'm getting about 9 fps. Turning anti-aliasing off has no effect on performance. Reducing aircraft shadows/texture quality has no effect on performance.

With scenery and autogen at normal, detail radius and all that stuff on minimal, I'm getting about 17 fps. Out of desperation I put everything on sparse and I was still only getting around 20 fps.

The only time I was able to coax a higher framerate out of it was by disabling high-resolution cockpit textures, and then my instrument panel looked like crap. Somehow the texture resolution is what's causing the problem, but I don't understand why, because Falcon BMS 4.32 also uses high resolution (actually double resolution) cockpit textures and I'm getting anywhere from 45-60 fps on average with that.

The ATI control panel has everything set to "application controlled," except for "enable surface format optimization." Anti-aliasing is set to multi-sample.

This really isn't making a lot of sense considering that my dad's old rig, 2.8GHz with 4GB of RAM and an integrated 5700 series card, was getting much better performance with high settings, and I'm getting horrible performance with low settings!

Anybody have any ideas?