Early 2013 Macbook Pro with 4K: Picture quality?
From Everymac


  This model supports a simultaneous maximum resolution up to 2560x1600 on two external displays via Thunderbolt. Alternately, it can support a single display up to 2560x1600 via Thunderbolt and a single display up to 1920x1200 via HDMI.


2560x1440 native on a 27" screen is just fine for my old eyes - I've got 2 of them here (screens and eyes ;) so 2560x1600 ought to be OK, assuming it scales down nicely.  

"Best" picture quality would theoretically be a native resolution of that, not scaled - but that wouldn't be future-proof; so you'd have to make that call.