One of the things I feel is important is matching your external displays with the internal one, the 1440p in the T470s matches up with all of my displays at every desk I work at. This makes it pretty easy to move around and feel comfortable.
So 1440p is fine, but once you end up in 4K territory it's nigh unusable. They've barely started on fractional scaling, so your choices are big or even bigger.
