The Unigine Valley 1.0 Benchmark is GPU limited. Very little load is placed on the CPU.
Have you run GPU-Z during the running of Valley to determine what speed the PCI-E Bus Interface is running at? Also check the graphics card's clock rates. Check the Sensors tab page to see what the PerfCap Reason is (i.e. could be Pwr: Limited by total power limit, Thrm: Limited by temperature limit, VRel: Limited by reliability voltage, VOp: Limit by operating voltage, Util: Limited by GPU utilization)