There have been issues using both graphics cards. You're better off disabling the Intel graphics and picking up a DVI to VGA adapter to put both monitors on the nVidia.
Well, I can't, because my GTX 660 Ti has only one DVI-D output. The other is DVI-I, which cannot be transformed into VGA.
I'll guess I'll have to wait before PPBM6 is released to benchmark and then maybe change screen.
The DVI-I can be converted to VGA since that is Analog or Digital. DVI-D is digital only and cannot be converted to VGA passively.