Will you be doing any hardware assisted encoding (using CUDA or the like), or will the encoding be done mostly by CPU? What sort of encoding will you be doing (ie how well does it multithread)?
If you will not be using hardware acceleration for encoding (and are not obsessed with high-resolution gaming), the video card may not be all that important.
My current favorite AM3 CPUs are the 1090T (6 core if your application multi-threads well) and the 965BE (4 core, high clocks possible). I know there are newer editions (1100T and 970BE), but I don't know that they are worth the price premiums.
If cost is not a huge issue, the new (Intel) Sandy Bridge chips are (surprisingly) competitively priced, and probably your best bet for best-case CPU performance. Too bad they don't have a 6-core model yet, or it would wreck the competition. Sandy Bridge also appears very power efficient. Lower idle power == lower idle fan speeds required.
Edit: Not sure that there are enough SATA connectors by default, but the Seasonic X-650 power supply should be mostly inaudible. Saw that you mentioned PSU noise! If you need more SATA connectors, it is modular, and I believe additional connectors are available (not sure about details).
Edit2:
danimal wrote:it's an intel/nvidia game, running anything amd in that scenario would mean more noise, more cpu heat, and much less rendering power.
Do you mention nvidia over AMD/ATI because of CUDA, or some other reason I'm not seeing. Just curious.