Yes, video encoding will decrease. I am currently in the middle of over clocking a 4930k myself.
As for, is it worth it: I am in the same boat ad well. Here's a few things you need yo remember:
The 4930k has a "turbo" of up to 3.9 GHz. But, that is only for a single core work load. Encoding uses all 12 threads you have (6 cores + hyperthreading per core = 12). So you'll be stuck around 3.4 to 3.5 on stock while encoding. Consider this your "base-line."
If you were to overclocked to a mediocre 4.2 GHz keeping all power savings enabled (Intel SpeedStep), that's an 24% increase in speed. That's huge! And 4.2 is easy to archive without batting an eye. Maybe a tiny bump in vcore. You can quickly start to see how much faster you can get. This would be an overclocked across all cores.
You're other limiting factor when encoding is your HDD. Even VelociRaptor drives in RAID 0 can't compete with a normal SSD drive in bandwidth, but especially seeking! Get under an SSD. Use your big storage to store, but use the ssd for encoding and move it to storage when done.
Now, there is a downside. The Sandy Bridge-E X79 chips' MCH was extremely sensitive to over clocks. MCH = memory controller hub. If you overclock, you most likely had to slow down your ram speeds to 1866 or so.
Now there are those with great memory that are able to run at 4.5 GHz and memory at 2400 all day long. Those are flukes! Actuslly, my 3930k runs great at 4.6 GHz and memory at 2133 all day long. Everything is left on Auto in the bios. I really lucked out.
The IB-E 4930k is supposed to allow for higher MCH speeds now, I think it is rated at 1866 whereas the 3930k SB-E was rated at only 1600.
The point is, be weary of over clocking and the memory holding you back. As a matter of fact, I'd put the memory at 1866 and go for ur biggest overclocked first. Once stable, then start to increase your memory speeds and voltages until it is stable.
1866 is nothing to laugh at either.
post edited by eduncan911 - 2013/10/12 12:18:46