The difference in contrast ratio is due to a black level of 0.018 nits on the 1080p version compared to 0.023 nits on the 4k model. This is unlikely to be a very noticeable difference as they are very good. The TVs do deliver very similar performance. The resolution detail that you will be able to distinguish also depends upon the size of the TV. Although you watch from a wide range of distances, 12' is quite far from even the largest of the D Series TVs, and you're unlikely to notice the higher resolution so go with the 1080p.