I am not too familiar with the technical details regarding the text rendering in ST3, but I can clearly see the difference between ST3 and Vim/GVim. At least on the machines I use (Desktop Archlinux & MBP OSX). Apparently ST3 uses Skia2d[1] for rendering which is what Google Chrome uses as well. Even for the text. But again, it's not just about the text rendering. ST3 is designed for the modern GUI and Vim/Emacs are not. What I want to see is the raw power of Vim + nice modern UI rendering/feel. It can't be that hard.
[1] - http://www.sublimetext.com/3dev (search for Skia)