I run Firestorm on a lesser spec machine with all settings to max without issue. Main thing is to have a good and fast graphics card, like you listed, and sufficient RAM... 8GB+
Windows 7 runs basically without a glitch, though noticed that on my machine teh SL viewer is significantly slower.
Now upgraded to Windows 8 pro, build 9200. Works fine, though like with any other Vista/win/ applications (MS Office 2012, Firefox, Adobe Creative Suite 5 etc... ) it sometimes freezes for a second or 2... but that is a win8 problem, not related to viewers