I would get the 2600k. Actually, I did get the 2600k, i was in the same boat as you got the 3570k and returned it when I found the 2600k for sale for $20 more. Most graphics cards are not saturating pcie 2.0 completely, which nets you no or very minimal benefits with going to pcie 3.0. Considering what you said you will be using this for, BF3, Crysis 3, and converting movies, all benefit from hyper threading. In my opinion, you will see a greater increase of performance from the extra threads, over pcie 3.0 for what you are doing.
Also, as these next gen games are being released, we are seeing more support for multiple threads, such as those games you mentioned.