Windows 7 and 8 (before 8.1) is not good at using 200% or larger DPI - it turns off the hardware-accelerated mouse cursor, which has the effect of changing the mouse acceleration as well (since it's controlled by Windows instead of OS X). So the maximum useful DPI is 199%, although the default mouse cursors and a lot of icons were only designed for 150% maximum, so they may appear pixelated or blurry.
Fusion 6 adds the ability to automatically set the DPI to 150% and enable Retina support by default, but in the end it all depends on the specific Windows apps that you want to use. There are many older applications that were only designed for the standard 100% scale.