I just pre-ordered the Panasonic GH4 and built a new monster editing platform to handle it. Shooting in 4k gives you more pixels and 4 times the bitrate giving you more latitude in post and captures more details. This is overkill for most internet clients however the company I am shooting for is more than just an internet company and is thinking about the future of broadcasting. Although it is currently pretty much useless to most people for porn in 10-15 years from now 4k will be what HD was 10 years ago. My camera was suppose to ship a couple of weeks ago but I am still waiting on Panasonic I hope to have it this month and shoot some tests like this against my 5D Mark III
Here is a test with the GH4 against Red Epic and 5D Mark III
https://www.youtube.com/watch?v=8kwMWb2KPB4
Make sure to set it to 4k on the settings. You can also download the raw clip.