Try the suggestions posted in the below linked article.
When in MacOSX if video quality is better,it is obvious that it is the software that makes the difference.
On the thread subject, like to note that I ran across this issue a short while back and there is an impact due to the hardware being used while experimenting with my Late 2011 15" MBP with widescreen antiglare option. Installed the gfxCardStatus utility that lets you know which of the two GPUs is in use and/or force a specific mode.
Ran VMWare Fusion normally and determined that it caused a switch to the Radeon GPU, regardless of the VM settings. Then, since I needed to run the MBP on battery for an extended period, decided to force the Intel GPU and ran Fusion again. The hypervisor loudly complained about being "unable to provide adequate graphics support to the VM and how some graphics capabilities would be impacted in the guest system". On the Windows XP VM, when running lean on the Intel GPU, images such as the background, icons, etc., did seem granier than when on the Radeon GPU. Text was ok, but did feel as if something was a bit "off". Even though screen resolution was maintained at the native 1680x1050 at all times
But nothing crashed or burned, XP worked fine. And battery life was significantly extended.
Will experiment with VirtualBox & Win7.