The PC version of Skyrim can really only uses two cores/two threads. 4GHZ is 4000MHZ or 4 gigahertz. An Athlon II X3 running at 4GHZ(the CPU was modified via overclocking to run at this speed) is probably faster for Skyrim than a Pentium G840,although I suspect the difference is not that huge. The HD5850 1GB is an older card which is slightly faster than an HD6850 1GB.