You might want to give build 7068 x86 a try. I had somewhat the same problem as you a while ago around when I was on 7022, except not so severe. I'm copying a DVDR9, about 7 GB to test for ya from my system drive to data drive (both WD SATA 150) and the system along with windows itself seems just as responsive as when not.
I can only say good things about the latest builds and have found as the number gets higher, so does the quality. So ya, 7068! Try it.