Did some more tests out of curiousity 
USB3 to NAS - 35MBps (pleasantly surprised as it was more than I expected) :D (N600 gigabit modem)
USB3 to USB2 - 30MBps (about what I expected)
USB3 to USB3 - 126MBps to 154MBps (stayed at over 150 for half the file) (completely contra to the first similiar test)
Tests done by alternating 2 files about 11Gb each (to minimise cacheing)
Desktop PC running Windows 7 64bit with 8Gb 2000 ram and 40Tb of discs (total) including 3 RAID mirrors. ALL my BIG files are on ONE USB3 XHDD (backed up on the NAS) so that was used as the source.
Mine is not bigger than yours, just reporting to anyone interested 
