Keeping this to prewar, as it should be...SGC has been on par for the non registry sets from what I follow.
Post war, there seems to be a strong consensus that SGC prices pale in comparison, probably due to registry. Well documented and widely talked about on this board.
As mentioned, boasting about a particular grade and its sale is probably always going to happen, and has a good chance to be stale news as soon as the next hammer hits. Way too many postwar high grade cards out there, and they seem constantly for sale.
So what?
Other than T206 whose availability rivals 52 Topps, SGC cards look to being doing fine in prewar. Maybe even setting records...