Personally, I'd spend $34 more for the GTX560 over the HD6770.
This EVGA card seems to support 2x Dual-Link DVI ports. It's
$128 after 10% off and $30 MIR on Newegg. I checked a bunch of GTX650/650Ti cards and I can't find any that support dual-link dual-DVI on Newegg. This is why GTX560 is the next best option as HD6850/6870 cards on Newegg don't support 2x DL-DVI (an no 7750/7770/7850 does).
GTX560 is about
56% faster on average than HD6770 for $34 more over the $94 6770.
The Zotac 620 is a weak GPU. I might have recommended the GT430 or Zotac 620 for someone who wanted to 2D but not 3D!
GTX 560 1GB (DX11) -- 119 VP
6770 1GB (DX11) -- 76 VP
GT 620 (OEM) 1GB (DX11) -- 23.9 VP
If you are on a serious GPU budget, I'd go for the HD6770
at minimum. 2560x1600 is a very demanding resolution. Can't take it lightly.