I went from 1200p (20") to 1440p (27") and the difference was huge. Part of that was the move from 4:3 ratio to widescreen, but the sheer amount of extra screen real estate is what blew me away. I'm glad I didn't try and go to 4k though as I find font sizes at 1440p just on the threshold of what my eyes are able to bear without needing to be scaled. Also, 4k would need a GPU that's out of my budget range.
A 1070 is ideally suited for 1440p. But you can get by with a 1060 or RX 480 for many games, especially if you stick to 60Hz, although you may need to step the quality down from Ultra to High in some titles.
144Hz vs 60Hz is very much a personal preference thing. Personally I've never had a problem with 60Hz and value colour accuracy over refresh rate (the choice was between 60Hz IPS and 144Hz TN with the budget I had available).