So i have two problems first of which is choosing a gpu for my 2 screens, will be gaming at 1080p and working at the 768p monitors so which of the gpu would be enough? And my next problem is would my psu handle it?
Cm 690 ii black and white edition
Fsp everest 85plus 600w
3 case fans
Technically, your psu will handle all 3 cards, but if you're still worried (that psu doesn't look that good) then I would stay with an nvidia gpu and get the gtx 670. It should perform the best out of those 3 anyways.
And all 3 gpu's will be able to handle max or almost max gaming on the 1080p monitor and be able to do other stuff on the other monitor. Being able to multitask is also more reliant on the cpu, rather than gpu - but you have an i5 so you're good.