I just need to be done watching [REC]2 (which I transcoded last night).
So what's the question? About clock speeds? An increase in CPU clock yields pretty much linear results. So an 8.8% increase in clock will make little difference. When picking out a CPU, there's usually a point where the price jumps up considerably from the previous increases from model to model. I buy the one just below that large jump.
As for over-clocking. If you're buying a chip well into the manufacturing cycle of a particular product range, it's likely that most of the chips are of very high quality, and have just been under clocked to fill the demand for the less expensive models. At that point they over-clock well, and are completely stable. That said, if you'd doing 12 hour renders, you don't want the machine to shutdown 80% of the way through for an 8% time savings. So be sure to do a prolonged burn-in before trusting an OCed part for production.
As I mentioned in my lead-in, I transcoded a Blu-ray rip of [REC]2 to MPEG2 for a DVD for a friend. These days I'm using PEGASYS Inc's TMPGEnc4. It can output DVD or BD ready video files. A couple months ago, I added a SpursEngine card (half a Cell processor on a PCIe card) to my PC, and the plug-in for TMPGEnc. Talk about a speed increase! Best $190 I've spent for a while. So I'm using CUDA for decode and filtering (resize, denoise, etc.), and the SpursEngine for encode. I'm seeing results pretty close to what is predicted by these graphs:
http://tmpgenc.pegasys-inc.com/en/images/spurs/txp4_Spurs_plugin_test_en2.gifIn closing, don't worry too much about the CPU. Put the extra money into some General Purpose Computing accelerator card (or two). I wouldn't bother with the Quadro card either. It's not any faster than the 285, just cost $600 more. If your software says it only works with the Quadro, find other software, because they're charging you too much too.
