Should I buy an nVidia GTX 770 or 760?

Get a 760. 760 can run most of the games on ultra. Use the money saved to buy a new GPU in a year or two to run newer games.

I've always been a fan of getting big strong cards right on the edge of the budget (and usually a little beyond XD) and keeping them for as long as possible. Given you that you had your previous system for 11 years I'd say you also fall into that category and then the 770 is a VERY clear winner. What's barely a frame or two apart now will stretch itself to being 10-20 frames ahead as time drags on and eventually will even amount to the difference between playable and unplayable frames and then that premium will pay off bigtime.

I had a X850XT for 5 years and then a GTX260 for 5 years and both times I've run out of graphics tech more so than performance (lack of newer pixel shader technologies both times) both times. However I was unhappy with the performance of the cards directly below mine both times long long before my cards started showing their age. Settling for a 9800GTX+/GTS250 cuz it was good enough at the time would have absolutely driven me up the wall during half of those 5 years unlike my 260 which occasionally still encountered a game it could run almost effortlessly (on my previous 1680x1050 22" screen).

So I definitely recommend the 770 over the 760 if you're at all like me. If not even trying to grab the cheapest 780 you can find like I did this time around.

Just built a new comp. I'm waiting till next month for the 880 though.