Had a similar kind of issue you're having, for a loooooooong time in fact - but Im at the office and cant remember exactly what I did to fix it.
Tried a lot of different things, and did find the problem... but I can nearly promise you that the fps you're getting is not what your system should deliver - as we've both got similar set ups.
First off; is there a particular reason why you don't expect Nvidia surround and SLI to be enabled? Different sized monitors perhaps? I only ask as mine is set up for surround and SLI - and I never found the need to disable - the problem was with DCS and the way it was trying to treat my monitors, not because of my current GPU configuration.
I also remember I had a huge difference in performance between full screen and windowed mode at the aspect ratio I was being defaulted at, for the resolution I wanted - 5760x1200 will automatically default you to a "4.8" aspect ratio, which seemed to give me trouble in fullscreen mode.
Are you simply trying to give yourself a wide view across all three monitors? Or are you trying to use the 2nd or 3rd monitors for MFCDs/other viewports?
If you're trying to set up MFCD etc etc - may want to look into some of the guides out there
http://www.digitalcombatsimulator.com/en/files/214771/
Disabling Aero just turns off some of Window's GUI effects - but you should not have to worry about that. I'll have to double check my settings when I get back because with your setup, unless you've got some underlying problem, you should be getting what I'm getting - which for me, is close to blowing the doors off performance wise
My config:
Windows 8 64 bit
ASUS ROG Maximus V Extreme w/Intel 3770k @ 4.5
2 Gigabyte GTX780s GHz Edition
16gb RAM 2400mhz Corsair Dominator Platinum
Running off a Samsung 840 SSD
3 24" ASUS IPS panels with at 5760x1200
Track IR/Warthog HOTAS/STK Pro Pedals blah blah I don't think the rest of my specs are going to matter too much -
I get there could be OTHER issues - but assuming you have a healthy OS and normal DCS install? Your rig should be handling DCS just fine - You've got the horsepower - but DCS can be a challenge, simply getting it to run across three screens - one wrong setting, and you'd wonder if you'd got 560's instead of 780s.
And for me personally, it had nothing to do with bottlenecks, on MY end - it simply was about the wrong aspect ratio/monitor setting/ or the way DCS treated my overall screen space - once you find it, you shouldn't be anywhere below 55fps.
I'll check what I had found once I get out of the office see if I can replicate my own issue (just hope I can fix it again :D)