This has been fixed by Teradici and the Horizon team in Horizon 7.12, which we released yesterday. Internal testing results:
GPU usage for NVidia is drastically reduced, from 2-3 times for a single HD display (5% before ->2% after) up to 10 times for 4xUHD displays (50% before ->5% after).
CPU usage is equal (slightly less, but within testing variance) to the old path.