Two things I've observed.
(1) At least one source mentioned 177Hz support for future G-SYNC monitors, including
Guru3D.
I noticed this number
exactly matches DisplayPort 1.2 single channel bandwidth of 8.8 Gbits/sec. (half of 17.6 Gbits/sec dual-channel).
1920×1080 x 24-bit x 177 Hz = ~8.8 Gbits/sec
(2) It gets better. When DisplayPort 2.0 rolls around, double the theoretical maximum refresh rate to
354 Hz. Or even if you limit to 177Hz, that could still be useful for faster frame delivery times from the GPU to the monitor, even when limiting the panel's refresh rate. Basically, 1920x1080 frames delivered fully to the monitor in a
mere 2.3 milliseconds of frame-delivery lag, regardless of current refresh rate. Basically, you use DisplayPort 2.0 at the maximum dotclock to accelerate frame delivery time to 1/354sec, even if you update the panel at only 144Hz, 177Hz, or 240Hz. Theoretically, you could even have monitor on-board triple buffering, too.
With G-SYNC,
the frame delivery time is decoupled from the refresh rate.
During 2014, there is no reason why we can't deliver individual frames to the monitor in 1/354th of a second, even if we send only 144 frames over the cable per second for a 144Hz-capable panel.