You should get around 7.20 on Cinebench at 4.4 GHz.
I have no idea what could cause this, maybe it's possible that something could be broken.
This is what I would do.
1. Update BIOS if available
2. Load BIOS defaults, set multiplier and voltage + memory leave others as is.
3. Clean Windows install
4. Install Windows updates and those two AMD related patches + graphic and chipset drivers, especially if I have not done a clean install after changing motherboard or CPU OR if resently installed Windows, check task manager that there isnt any funky applications.
Oh, on Windows task manager -> performance tab, does it show all 8 cores there and all of those have full load when running prime?
I assume you don't watch Blu-ray, have utorrent downloading next one and doing a full virus scan while benching?