If resolution is what you're worried about then just try downsampling when you get your rig.
I currently use an NEC 24" workstation monitor and on certain games that don't offer resolution scale I downsample to 2560x1600 from 1920x1200.
So basically if you're running that 770 4GB you can create the custom resolution and see if you can downsample 1920x1200 or even 2560x1600 on your current monitor. Note, that this only looks good in games and not the desktop.
If I was at a split decision between more GPU horsepower or a higher resolution monitor given the fact that I was already using a 20" 1680x1050, I would go with more GPU power personally. But that's only because I've been in your situation before.