I don't know about whitepapers, but the general consensus around here seems to be that Win7 is a worthy upgrade (especially from XP) and if you can wait for a couple of months it's probably worth it to install Windows 7 directly rather than install Vista now and upgrade later.
On the other hand, there is no "upgrade" from XP to Windows 7 - you have to install from scratch. So if you want to avoid the need for a complete reinstall, you may be better off upgrading to Vista now and then upgrading from Vista to Windows 7 later.
Mind you, I don't think I'd want to have a doubly-upgraded system, but it's really up to you...