I'd look into bg apps attempting to go fullscreen before I started ripping out hardware, check the rig in my stats, it's not far off from yours so assuming none of your hardware has shit the bed it should be fine.

One of the most commonly missed DX fullscreening issues are screensavers, if you play w/ a gamepad the input from it doesn't count toward non-idling so your screen saver can/will still try to kick on killing your fullscreen. I don't know wether or not this game works like XI controls-wise but I know that XI hooked the input controls so that mouse/kbd messages never made it to windows, so that even though you were mashing keys your SS would still kick in.

So basically > Other apps that are running > screen saver settings > hardware check.

Since SE doesn't want to get onboard with dropping and reacquiring screen device contexts like every other game on the market those of us who'd rather play in FS but still want to be able to alt+tab from time to time during longish sessions get the shaft. Even more so we lose out on Crossfire/SLI or get stuck in FS and have to exit game to check e-mail.

In it's present state I get the same(and sometimes better) frame rates in windowed mode on my rig. Again yours isn't that different it might be worth looking into, use a pseudo mode app to make it FSish, here's the one I use, it doesn't break ToS all it does is stretch and reposition the window, it doesn't interact w/ the game at all.
Shift Window