I own a computer shop and people where asking for Windows 98 on a Pentium 4 - 1.4GHz with 256 or 512MB RAM!
Regarding WM5, agreed, I'm only talking about a stable version (whether it's official or not). Mind you, the WM5 we're all waiting for IS MEANT to run on the Magician as it was specifically built for it. Otherwise it wouldn't work in the first place.
And according to Microsoft, the Magician meets the WM5 minimum requirements, mainly being an Xscale compatible CPU, 64MB RAM and 64MB ROM.
Samsung Galaxy Tab 10.1 P7510
Samsung Galaxy S3 (i9300)