Back in december 2012 I've benchmarked (shortly) native and virtualized Mac OS X against virtualized Windows.
Few days ago, I've dedicated a 250G B SSD to a Windows 7 installation, inside my Mac Pro. Weird thing for me to go back and forth between Mac OS X and Windows. I'm more accustomed to +50 days long uptime. Admittedly my various attempts to put Mac OS X into deep sleep, reboot on Windows, and go back later to a fully restored Mac OS X session right out from deep sleep, are failing. That's another story.
Nevertheless, I'm using this Windows system as a playground.
Inside this Mac Pro model 2010, I've one Xeon quad core 2.8 GHz with 24 GB RAM, and a Radeon HD 5770. One SSD is dedicated to Mac OS X 10.6.8, and one SSD is dedicated to Windows 7 Pro 64 bits (with latest stable Catalyst drivers). Both systems are using the latest Steam client with a fully updated and clean Left 4 Dead 2 install.
I've recorded a demo, and played back this file on both systems with identical video settings, recording fps numbers during the playback. The demo is 17827 frames long, and video settings are "MSAA x4", "Anisotropic 8x", "vertical sync triple", "resolution 1920x1200", "shader detail very high', "effect detail high", "model/texture detail high".
The playback is a bit laggy on Mac OS X, especially when the player is looking at fire. It would be playable, but not a very smooth experience. The playback is better on Windows.
Here is the plot of numbers of frames calculated at a given fps rate. For example, on Mac OS X (black line) a total of 4 frames were calculated at a frame rate of 10 fps. On Windows, 90 frames where calculated at a frame rate of 47 fps.
Windows 7 has better drivers, and may be the game itself is coded better. The fact is some situations in the game are not handled very well by the GPU on Mac OS X. The huge spike around 30 fps means that ~2500 frames were computed at about 30 fps. Not good. But more importantly the global shape of the plot shows a spread of fps values from as low as 10 fps to 60 fps. Note that the log scale on Y does mask isolated frames (Y=1).
Windows does a better job here, with only a handful of frames below 40 fps.
Fortunately L4D2 is an old game, and my hardware is enough to handle it nicely even on Mac OS X (I usually play at 1600x1000), but being able to push it a little further with full quality on Windows is a nice thing. I hope L4D3 will run ok too, some day, in a not too distant future.
To complete the comparison, I've made a Cinebench R15 benchmark. The OpenGL score on Windows 7 is ~64 fps, and the same test on Mac OS X 10.6.8 is ~53 fps. On CPU side both OSes score around 440.