You can't compare CPUs based on pure Ghz.
You can probably use a combination of AMD components with an older NVIDIA
graphics card. It probably won't give you quite the same user experience.
You would also want to find a motherboard without built-in graphics. Your
probably looking at a more expensive motherboard. If you saved $100 USD on
the CPU you may end up putting that into the motherboard.
If you wanted to try and put something more freedom friendly together
although also bad (in terms of supporting two entities which come out very
anti-free software) the NVIDIA + AMD CPU (/w out internal graphics) +
coreboot might work (but you need to take a look at the list of coreboot
supported motherboards). This isn't a simple task as most of the motherboards
are no longer in production which will make them harder to find and more
expensive. Many of the coreboot systems are server oriented too I believe.
