@MattDUsing either of those settings how long does it take you to generate, say, a 10 (or 15, or 30 - so I can extrapolate) minute video? I've got a less powerful PC than you, an i5 Quad Core (no hyperthreading) 2.9GHz 16Gb and it still renders in far more than real-time (so a 10 minute video takes about 20 minutes, in H264 1080P 25fps).
If I generate a MPEG4 video at 20 fps .mp4 it takes about 75% of real-time (so a 30 minute video takes about 20 minutes to render, or thereabouts).
Hmm, I've just seen that AMD are to bring out a 16-core monster in the summer to rival Intel's i9... :o