The GRCS is well within the SWL of 5/8ths dia. Stable Braid rope. The winch can easily accomodate this size rope for most tree work including lowering. You can do some lifting with this size rope, pretensioning a double braid is usually about all you would need to do with the winch to lower out some big logs. 1/2 in. dia. is better suited for long big lifts because you can get more wraps on the winch than you can with 5/8ths. The more wraps on the winch the more traction you will have with no slippage. 1/2 in. rope will easily get 90 % of a tree down to the ground.
3/4 in rope is overkill for most average tree work unless your working on those big conifers in the PNW. 3/4 in rope is a pain to handle, tie knots, and is heavy If you think you need to use 3/4 in rope your either taking the butt end of some very big limbs or your blocking down some very big trunk sections. There is no need for the winch as this is simple lowering and the bollard supplied with the GRCS will easily handle these loads using 3/4 in rope.
As JP pointed out in that video they were pushing those lowering devices to the limit and they were adding slack to increase the dynamic loading on the devices. Both the Hobbs and GRCS were damaged but the ropes and knots failed more than the devices. No one in their right mind would do what they were doing to their equipment.
Get your hands on the video that actually shows how to use the GRCS. It clearly demonstates why the GRCS is more popular than the Hobbs.
Larry