Windows 7 RTM on MSDN

They posted it yesterday and I just confirmed it's there. Now the decision for my OS testing system: do I erase the Vista 64 that's on there now and replace it with Win7 x64? Should I try upgrading it? if I erase it all the Virtual machine OS's will be destroyed and I'll have to rebuild them -- or maybe not -- I can just save the virtual OS files onto a backup and reinstall Virtual PC and reload them. And does Microsoft's Virtual PC 2007 run on Windows 7? I know it can host it. Questions...