I don't know where exactly this came from, but it supposedly a side-by-side comparison between ROTR's 4K mode on the Pro and 4K maxed out on the PC:
Looks like the 4K mode will be lacking ambient occlusion, or at least it will use a form of AO that is substantially inferior to gameworks' VXAO in IQ.
Here's a close-up of Lara's face (sides were switched)
As for the resolution alone, for people sitting >1m away from a 4K TV it will be a bit hard to notice the difference between "real 4K" and 1440p + checkerboard upscale. Especially with things in motion.
Hopefully, we'll be putting the jaggies behind us completely within the next few years.
2*1080p is two 1080p screens side-by-side and the result would be a wider rectangle (32:9 instead of 16:9).
4k is two 1080p screens side-by-side on top of another two, so that aspect ratio is kept.
http://www.extremetech.com/wp-conte...-Digital_video_resolutions_VCD_to_4K.svg_.png