Im on the same boat. Then I dont know where you saw a 280x benchmarked overall better than a 770... The 770 is indeed slightly faster overall.
But Im debating the same thing 280x or 770. Was dead set on a 280x. But I am going with Nvidia for once. Was so happy with my current Intel upgrade(did AMD for over a decade), that Im am starting to REALLY dislike AMD. Mainly for problems Ive had with their hardware. Hell current problem with my 6790 is "Payday2, force AA/AF thru eyefinity and then load payday2 and watch your screen blur pure white and you cant see nothing" was the nail in the coffin for me.... Only thing I like about them now is competition to keep prices in check.
Only thing that makes me debate the two cards, is the vram sizes. If the 770 had 3gb or more at $330 or cheaper, then it would be a no brainer. Then givin how good bf4 runs without mantle for me, I dont really give a care for it and think it WILL not be the game changer, that it is being built up as.
But shadowplay interests me alot. Physxs is just icing to me, dont think much of it. Then gsync seems like bliss to me, for I hate my screen tearing in certain games(arma2/dayz). Then Im also in the market for a new monitor, waiting for more gsync models.
Only thing I can really hit Nvidia for, is they seem like d*ck Heads.... But I guess if my stuff was better than everyone elses, that I would seem like a d*ck too...
Far as 2gb vram vs 3 or even 4gb. Every single benchmark i seen shows no true difference. But then I read "word of mouth" about frame drops from vram, but NEVER seen it benchmarked....
Then givin my current card is only 1gb vram. I play bf4 med to high, my vram is in full use. Then I DO NOT see any huge framedrops. I bet you would with mods in skyrim, because thats not made by the developer.
Untill someone can show it benchmarked, Im leaning on this not being a HUGE issue as some say. But rather for future games with multiple monitor setups or ridiculous resolutions.
On that note. Im waiting for black friday. Probably will not see a 770 on sale, but heres hoping for a 770 with 4gb vram on sale. Otherwise Im going with a 2gb 770, unless the 4gb versions creeps below 350... Any higher and I might as well wait and buy a non-reference design 290(non-x). Which nvidia has no better offering at that price point.
Then currently the 770 comes with 3 games that I would like to own, but never pay full price for. Which is why I dont own those games. Where as with amd, I own any game on there that I want already. Then they do not offer it currently on the 280x.
My first post about this, after almost 2 months of daily research.... So enjoy my somewhat book of a rant