Hi. I have a dual boot machine with OS X Mountain Lion and Windows 7.
I played the Tuscany Unity demo on both operating systems, using the same exact hardware, and noticed that the OS X performance and image quality is lower than in Windows.
Framerate does not drop below 60 fps in Windows. But in OS X, I'm getting between 40 and 60 fps depending on where I am in the demo. I also notice some stuttering with the headtracking in OS X, and lower contrast and more blurring of textures and some other small graphical things that aren't there in the Windows version.
The hardware is the same. C2D processor with Geforce 640. Is there a reason why the experience is different between operating systems?
I'm not the expert on this by any stretch, but I would guess that it's related to the OS's graphics library. Perhaps Lion only has an older OpenGL version (I seem to remember Mavericks being announced with a newer version that would effectively catch it up with Windows or something), but your Windows 7 install lets your card stretch its legs with more DirectX capabilities, and more stuff being done on the GPU instead of the CPU?
I'm just making wild guesses here, and I'd like to know too.
I also dual boot my MacBook Pro, and there's definitely a performance difference. Games just run better on Windows, with higher detail options not degrading performance nearly as much.