The DGR is just the retail variant, but it has no difference from the DG, for me I would take the S2716DG, it's easily overclocked to 165hz, G- Sync, and 1440p, the only thing the U2717D has over the S27 is that's it's an IPS panel
TN has come a long way and the panel in the S27 is a VERY good TN panel, I'd even go so far as to say it's better looking than $3-400 IPS panels after calibration, it's sold out on the Dell site but it's $449 at Best buy right now