With the benchmarks out of the way, we can turn to tuning Parallels 6 Desktop for Mac for the best performance for the guest OS.
What we found was that memory allocation had less effect on the performance of the guest OS then we first thought. What this indicates is that Parallels' built-in caching system, which is designed to aid in the base performance of the guest OS, works very well, at least for guest OSes that Parallels knows about. If you choose an unknown guest OS type, then Parallels caching may not work as well.
Therefore, when setting memory allocation for the guest OS, the key to determining the size to use is the applications you will run in the guest OS. You won't see much improvement in basic non-memory-intensive applications, such as email, browsing, and word processing, by lavishing memory on them.
Where you will see benefits from upping the memory allocation is with applications that do use a lot of RAM, such as graphics, games, complex spreadsheets, and multimedia editing.
Our recommended memory allocation then is 1 GB for most guest OSes and the basic applications they will run. Increase that amount for games and graphics, or if you're seeing subpar performance.
By far, this setting has the most effect on guest OS performance. However, as with memory allocation, if the applications you use don't need a lot of performance, you're wasting CPUs/Cores that your Mac could use if you increase the CPU/Core assignment unnecessarily. For basic applications such as email and web browsing, 1 CPU is fine. You'll see improvements in games, graphics, and multimedia with multiple cores. For these types of applications, you should assign at least 2 CPU/Cores, and more, if possible.
Video RAM Settings
This actually turned out to be pretty simple. For any Windows-based guest OS, use the maximum video RAM (256 MB), enable 3D Acceleration, and enable Vertical Synchronization.
Set the Performance setting to 'Faster virtual machine.' This will allocate physical memory from your Mac to be dedicated to the guest OS. This can improve guest OS performance, but can also reduce the performance of your Mac if you have limited memory available.
Turning the Enable Adaptive Hypervisor feature on allows the CPUs/Cores on your Mac to be assigned to whichever application is currently in focus. This means that as long as the guest OS is the foremost application, it will have a higher priority over any Mac applications you are running at the same time.
The Tune Windows for Speed option will automatically disable some Windows features that tend to slow down performance. These are mostly visual GUI elements, such as slow fading of windows and other effects.
Set Power to 'Better performance.' This will allow the guest OS to run at full speed, regardless of how that will affect the battery in a portable Mac.