I am on XP Sp2 32bit
Cubase 6 runs perfectly alongside 4 here. Almost everything transferred into C6 automatically except for…I can’t remember now, either my custom keyboard shortcuts or preferences. I simply located the relevant file in C4 and copied to the equivalent place in C6 and selected.
That was in January. The only problems I have experienced have turned out to be either my ignorance of changes made in C5 which I bypassed, or a few graphics things which I had to adapt to be comfortable with ie. 4x2 toolbox, event display etc.
I moved to C6.01 on its release. For me it’s the most stable Cubase to date. The only crashes I have suffered, I attribute to a dying CDRom drive and a dodgy plugin.
Best to mirror your drive if possible, or at least set a restore point.