Off the top of my abnormally large head...
1) If you want to compare performance you should start by posting your game settings and actual bench results
2) FPS limit is not tied to v-sync but to UE3's "framerate smoothing":
%USERPROFILE%\Documents\WB Games\Batman Arkham City GOTY\BmGame\Config\BmEngine.ini
bSmoothFrameRate=TRUE
//set to FALSE to disable smoothing completely...MinSmoothedFrameRate=22
MaxSmoothedFrameRate=62
//...or simply enter a higher value here (80, 999, whatever) to keep the smoothing but lose the cap. I set it to 162.3) Does the game work OK with 4 cards ? Did you measure SLI scaling with 2, 3 then 4 cards ?
4) If SLI scaling sucks, PhysX set to High will only make matters worse (by all means give 3-way + dedicated Physx GPU a whirl).
5) DX11 FX are very resource-hungry and may not mix well with SLI, esp. with 4-way SLI
and in Surround.
6) There's a lot of data streaming going on in the benchmark (next scene is prepped before current scene is over), so framerate dips are to be expected.
My config:
i7 4930K (3.4 GHz), 16 GB RAM
780 Ti (2-way SLI), nvidia driver 332.21
10K RPM HDD
Windows 7
My settings: all High except tesselation (Normal), FXAA High, 6060x1200
My results: Min 36, Max 120, Avg 77.