Hi,
I know this thread is a few months old now but I have just com across the same problem. I have just built a rendering PC for use in a school with an Intel i7 3960 @ 4.5GHz, 32GB RAM, nVidia 570GTX and WD Caviar Black OS HDD (1TB)and rendering HDD (2TB).
I was using Vegas Movie Studio 11 HD and downloaded Pro 11 trial to see if it would render any quicker, being 64bit. The same project actually rendered 10 mins slower than the 32bit home version!
Anyone have any ideas why this is?