I used to play beta/release at 1920 and also doing videos with fraps at the same time, all with my old 560gtx and fps were fine.
Then with craglorn patch something broke and later with 1.2.3 something was terrible more broken.
Of course all add to the problem (zerg balls, camps used as tp, AOE heals spammed to get ultimate, etc) making people coming more clustered, but that wasn't a problem in release.
Today to celebrate the EU server migration I bought a new gtx 770 and of course the problem persist (i knew it before purchasing).
The thing is that if I are alone or with very few people around i get 70-90 fps, then when there is a moderate group fight of 15-30 people the fps go down to 35-50 and when there is already more people(30-60) the fps go down to 20-29... ofc in big action sieges the fps can drop to 15... THIS DIDN'T HAPPENED AT REALEASE/BETA WITH v1.0 ... i played way better then with my 560gtx than today with my 770gtx. (of course that don't happen only to my, you just have to read the chat or speak with guildmates).
I am not talking about the lag here (also an issue), i am talking about the fps lost that happens when there is people/battle near you, even if you are not watching the fight or you are not there, even if you put in first person and stare at the floor... you get 20 fps, only for being near a battle.
The thing is that nowhere in 1.3 notes says that there is a fix for this... and the old post of (hotfix for fps lost) has been unsticked and lost.
So there is someone at Zenimax looking at this please ? even only acknowledging the issue its good for me.