So as title says would you say for 1600x900 a gtx 770 2 GB is enough or should I go for 4 GB version? I have like 150 dollar cheaper deal on 2 GB so if it is OK for this res I don't want to exaggerate the future need and go for 4 GB for this res.
Yes I am going for all ultra maxed out since I assume it is capable at this resolution with these specs am I wrong?
No, you are not. However, in case you got stuck with your vram and it was the factor limiting your gameplay, there is some pieces of advice if you dont know them already. The vram is mainly consumed by high resolution and anti-analysing options and its varieties (MSAA,FXAA,etc), so if a game performed bad and you managed to know that the vram was the reason(gpu-z is very good gpu monitoring program), then it will be recommended for you to turn down some AA or lower your res(which i dont prefer, the game will look awful). As far as i am concerned, the only games that uses more than 2gb of vram AT 1080p 1920x1080, are crysis 3 Ultra 8xMSAA(most demanding form of AA) and skyrim with TONS of mods, so at your resolution, the 2gb will survive for pretty long time, the important matter, is that your card might be old and some other limiting factors might appear before all of the vram is used up, and i doubt this will happen with the gtx 770.