And.. easy fix. The included Dell DisplayPort cable wasn't capable of displaying a full 165hz signal, but Dell must have rigged up some ability for the monitor to forcibly display 165hz (164 with free/gsync enabled) with a displayport cable attached no matter what.
Just swapped the cable for a DP1.4 cable (the bundled cable is 1.2), and the problem is resolved, now running full resolution at 164hz with zero text rendering problems.
As an aside note for anyone finding this thread in the future: The included HDMI cable was able to display full resolution at 144hz, but not anything higher. This also means you will not be able to fully enable freesync or gsync, as this requires a DP cable.