I run my P50C490 (1366 native) through an HDMI input labeled "DVI/PC" from an HD5450 at 1360 "Basic desktop" resolution at 1:1 pixel mapping (with 3 dark pixels on each side). The tv reports 1080p60 signal.
I remember initially, at installation (Win8-64) the signal was automatically set to 720p, however after setting a 1080p "HDTV" resolution from CCC, restarting, and re-setting to 1360 "Basic", the 1080p60 was retained.
My previous tv, a Vizio, could actually receive a 1366 resolution, matching the native with 1:1 pix mapping.
Both resolutions were available under "Basic" desktop resolutions, however setting 1366 with the current tv reverts to 1360.