I don't have an opinion about the GR HD but I can tell you that they all look great in the store and seem to be quite functional out to the "easy" distances when the light is good.
When the light is poor or the distances are great, you need the best of the best (like outlaw said, a 280 bull at 2 miles, type best). I too have seen that in action.
I watched a guy (who was with us, thankfully) on a desert sheep hunt actually use his spotter like a spotter. He never took his eyes away from the glass for hours at a time and saw a ton of desert rams that I would have missed! Live and learn.
Zeke