What I would say about Gsync is I never noticed it until I didn't have it so to speak.
I always just accepted screen tearing in some games (Just Cause/Crysis/FarCry etc) and never noticed it at all in others, racing games for example (F1/Dirt/Grid).
The I got the Acer XB281HK and after a day or 2 I thought yeah the games look really good but not spectacular. Went back to my Samsung 1440p PLS and the tearing was unbearable, I couldn't believe how big a difference it made.
Obviously when it comes to the Premium it's entirely up to the individual but for me it was worth it - especially for the racing games. I don't know if it's the gsync or the fact that I've gone from a PLS to TN a panel (and thus achieving a lower Response Time) but I have DEFINITELY got quicker at them, F1 2014 in particular, or maybe it's just my imagination!
FYI I picked my Acer up for £425 so got a good deal anyway.