I dont have surround setup, but you need to remember that 3840x2160 is 4 x 1920x1080. So it's not even close to "triple-wide" but more like "quadruple"
You can always simulate the behavior of your system at 3840x2160 by creating custom resolution in nvidia drivers.
Run the fps benchmark in fraps and see for yourself how big the drop of the framerate is.
EDIT:
I created custom resolutions in Windows XP.
I did a very quick test in
Burnout Paradise. It natively supports 5760x1080 and 3840x2160.
Mind you i have a weak PC: C2Q q9300 @ 3.0gHz, 4GB DDR2 RAM, GF GT640 2GB.
SSAO - OFF, AA - off. The rest was maxed.
4k indeed lowers the framerate.
when the car was standing still in a very quite place, the framerate at 5760x1080 was 49-50, at 3840x2160 it was 43-44
In action i was getting:
at 5760x1080 Min - 30, Max - 58, Avg - 43.903
at 3840x2160 Min - 22, Max - 49, Avg - 36.237
another quick test:
at 5760x1080 Min - 20, Max - 53, Avg - 43.352
at 3840x2160 Min - 16, Max - 48, Avg - 37.435
You will be better off with your own setup in more modern games. Burnout Paradise PC ver. is from 2009.
Here is the DR, if you're interested
http://www.wsgf.org/dr/burnout-paradise