Re: As someone still running Windows XP x64 ...
I run XP x64 on 3.6GHz Ivy Bridge Xeon E3-1280s, with 32GB of RAM. More than quick enough, even by today's standards. It's plenty "modern". By the way, I do have AHCI drivers installed on all my kit - I don't install it with IDE mode, simply because it's easier than finding a USB floppy drive and the F6 button on my keyboard. I do it properly, and 5 minutes of effort at install time yields astounding performance every day I use it.
If your last sysadmin was incapable of installing XP properly, that's hardly the fault of the operating system now, is it? He or she probably didn't align the disks to 64k+, either, so it would seem you're not comparing apples with apples.
On the other hand, the Windows 7 POS that I'm forced to use at work is slow (despite running on newer hardware, albeit with half the RAM of my home system), unwieldy - and why it takes bloody ages to open up my Documents folder, I'll never know. With XP, it was click-click, and you were there. With Windows 7, there is a large pregnant pause every time I open up my home folder, and I for one don't appreciate it.
The GUI in 7 is also worse, but that's not as bad as the sheer performance cliff, even on newer hardware.
Sorry, but I'm not buying it - literally or figuratively.