Thanks, thuan, for your answer.
I'm very surprised to find out that Xeons are simply "better tested" i7s!
I'm afraid to go Xeon because it's an "orphan environment" - much less knowledge on the Internet and forums, motherboards and cases with server form factors, much less selection, much higher prices. Of course, for larger organization this makes prefect sense but I'm working by myself...
Tempting as it is, I also don't plan on using two processors - one with HT and 4 cores (e.g. i7) would do fine. I need a development machine, not a multi-user server. The machine would run VS, Office, Subversion, CI, SQL Server and Web Server, each on its own virtual machine, but this load is not too high.
What I wanted to check is whether I'm missing some important capability for virtualization found in Xeons and server motherboards and missing in desktops. From your answer I gather this is not the case, so I'd stick with the i7.