Disabled HyperThreading? Set MSCONFIG to Diagnostic start with exception of Nvidia service? Other than that all I can think of is your vram clock. Based on your numbers, 1300MHz GPU with +800MHz memory gives better numbers than a 1500MHz GPU with +200MHz to memory. Which...makes sense. But just means you should dial back the gpu if you need to, in order to get your vram up. For single-card runs, it's surprisingly important.