Win7 is actually a slightly slower operating system than XP. The big increase in speed you're seeing is because of the hot rod hardware you're using now. XP machines might start to have more and more problems as Microsoft stops updating them with security patches, and newer software insists on a more recent OS in order to install.
Enjoy your new machine. Like you, I'm just in the process of getting ready to switch my primary computer from an old, reliable machine to an entirely new one.
Windows 7 have superior memory management. This reason alone is worth upgrading.
It is true the file copy is slow on windows 7 but there is programs like extremecopy etc...that will make file coppying fullspeed.
7zip is faster then winrar..
Windows 8 is faster on very old machines (and new) compared to windows xp.
So there is now absolutely no reason be stuck with XP anymore.
Windows 8 work better for DAW computers...Lower DPC latency etc
XP will soon stop offering free security updates... they will only be available for people who pay for 1 year subscription...
I have Windows 8 on a notebook and I find it unintuitive and confusing after having used every other version of Windows including 3.1. Also the touch interface is NOT needed on a desktop computer and there should be a way to dispense with it; I believe there is in 8.1.
It is very quick to boot though.