Sure many years after the initial botched, insecure, bloated hardware release it is finally becoming an OS people can work with.
Congratulations in finding that your card is faster than with Vista.
Vista has an excellent system for auto optimizing the receive window and MTU on the fly, whereas previous versions of Windows required manual tweaks.
I don't know how or where you tested your speed, but I'd say that your stats are inaccurate when you are saying 3X faster.
You were either grossly low on RAM, typical of retail products, were hitting the test servers at the wrong times of day or were runnign eh full bloat version of Vista without optimizing the OS itself.
XP is not a bad OS NOW (SP3?), but there's no way you can make a case against Vista by suggesting that Vista doesn't optimmize its network speedsas well as XP; not unless you can substantiate it with facts other than YOU managed to get your XP card working faster on YOUR connection.
How much effort did you put into tweaking Vista itself (not the network card but the OS)? I'd think that, as an XP user, you have spent many more hours working on getting XP to run as you like it over the years than you ever did with Vista. I think you just quit due to peer pressure and media hype.