If I remove those two lines, I get 1920x1080 again, but then I get the overscan.
I get a lot of this throughout the Xorg.0.log
The EDID for Tech. Concepts RCA (DFP-0) contradicts itself:
(WW) NVIDIA(0): mode "1920x1080" is specified in the EDID; however, the
(WW) NVIDIA(0): EDID's valid HorizSync range (39.000-49.000 kHz) would
(WW) NVIDIA(0): exclude this mode's HorizSync (67.5 kHz); ignoring
(WW) NVIDIA(0): HorizSync check for mode "1920x1080".
It really does sound like the OP is having the same issue I do. If I try tweaking the resolution of mine more than 1 pixel one way or the other, then I get "Unusable signal" Though on my end, it looks like X itself starts fine.