Those who are interested in learning about the different Avid codecs can read this white paper:
To me, DNxHD220x is essentially identical to Apple ProRes 444 HQ. All the major networks I know of have blessed these formats for post, but it's a good idea to check first to make sure the workflow agrees with what the network or channel wants.
If push came to shove, I would always prefer color-timing from a 2K 444 DPX file, and once the color-correction decisions are finalized, load in the 4K uncompressed files for the final render out. I don't see a need to monitor 4K 100% of the time, because of the huge performance hit you get on most color-correction systems. No doubt this will change over time, and eventually you'll be able to handle dual streams of 4K 3D with 20 layers without a hiccup. But not today.