just tried this yesterday with a 650m on a laptop....
frames dropped up from 40 to 75 fps (also did some other settings cause it wasn't set there before)
i did'nt noticed a latency problem, but also did'nt focused on that.
i think if you really need this extra performance then latency shouldn't be the problem in most cases
MainSys: Z77 UP5,3570K,32GB Ram,GTX 285, M3 128GB,4x3TB R5@LSI9750
VJSys 1: 990FX UD5,X6 1045T,16GB Ram,GTX970+610+610,M3 128GB,3x1TB R0
MBP 3.1; Schenker A102 (650m) & P702 (675m)