It does allow you to do a corehack and get bigger WUs, but where it applies to most people is just that Linux is better at folding than windows no matter what type of WUs you are folding. I tend to think of Linux as just having less overhead than than Windows and therefore allow your CPU to work more efficiently without the OS getting in the way. It's usually worth around a 10-20% improvement going from windows to a linux VM even with just regular SMP workunits. You ought to know VMs aren't just for corehacks Phil. Here is the VM guide
I like to use. I've had that take a 3.3Ghz 920 from ~12K in windows to ~15k PPD in the VM.
What would also increase your PPD a bit would be switching to advmethods WUs on the GPU, but they bring the drawbacks of being both hotter (by about 8c) as well as more likely to reveal an unstable OC. The plus side is that they use much much less CPU processing time so that your CPU PPD will actually go up as a result, a regular GPU WU can use as much as 5% of my 2600k but the advmethods WUs use between 0-1%. In my case that has increased my CPU PPD from about 20-22K to about 30-33K with just that change alone, you may not see such a drastic increase but it will still be considerable. To set up the advmethods WUs I'm going to assume that you're using the v6 systray client and tell you how to set that up, but if not then just tell me what GPU client you are using. With the GPU folding running right click on it's icon in the systray, select configure, go to the advanced tab and in the "advanced client parameters" field at the bottom you want to input "-advmethods" without the quotations. Feel free to post back if you have any questions.