Windows 8 allows for 128GiB on the base edition and 512GiB on the professional edition. Given that it's a newer OS and has a cheap upgrade path, I'd consider checking it out.
I've been using Windows 8 for months, it works great. I have yet to run into a single thing from Windows Vista or Windows 7 that fails to work under Windows 8. Even most device drivers will work.
EDIT: The Creative Labs X-Fi Titanium Fatal1ty and X-Fi Titanium HD sound cards work with Windows 8. The drivers are a little bit buggy at the moment but they do work provided you don't restart your PC very often. I'm not sure about the legacy PCI X-Fi cards though