I installed my GTX 560 (Non TI) about a year and a half ago with MultiBeast 4.5.1, in OSX 10.7.5. I've installed the CUDA and OpenCL enabler but I've always had the problem where I cannot get 1:1 pixel mapping - I am running Dual 27" 1080p Samsung monitors, both from DVI outs.
I am dual-booting OSX Lion and Windows 7, and the pixel mapping works perfectly in Windows 7. There is an obvious difference in picture quality as I've had to stretch the screen in OSX but I've lived with it for now, but before I buy a new graphics card (probably Radeon) I wanted to see if there were any ideas to fix this issue with the GTX560.
I posted this problem last year when I first made the install but couldn't fix the issue.