Before you go off investing in new hardware, you need to take a hard look at your current system and figure out what's currently your limiting factor.
While you are editing video, have task manager open to the detailed performance information. Not knowing your current software package being used, we don't know if it's very multi threaded, or heavily single thread bound. If you go out and buy a six core processor with a poor clock ceiling, and your software is heavily single threaded, you're likely to see very little improvement in your software performance. What you are looking for is in task manager, with logical processors listed, are you seeing one or two processors pegged at 100%, and the rest barely hitting 20%, then you are single core bound and need a major boost in clock speeds. You'll likely want the 10600k, or, if that's out of reach, the 10320 for now.
If, on the other hand, you're seeing four threads or eight threads equally loaded, then your software is well threaded, and the 10400 will give you a notable improvement. However, if that's really the case, then you'll see your biggest gains with going for more cores. Unfortunately, now is an absolutely crazy time to be looking for more than six cores because everything eight cores and above, with SMT, is selling for obscene prices. You can't even get a new 2700 for under $300 right now from any of the big sellers.
So, take a hard look at what's going on with your current computer before you spend and money on this.