"Appreciably" thicker is subjective... but, yes they do feel different, and the individual panels are a bit thicker than the one piece 3rd gen grip.
But they are not as thick as Hogue grips.
I think it's the back strap that makes the older double stack guns feel so 2x4'ish.
Maybe this will help... I have Uncle Mike's grips on my 459 & 559 instead of the factory panels, they are a bit thinner. The measured width of the factory grip my 4006 is 1.24 inches, on my 459 & 559 it's 1.39 inches... so that's only a .15" difference.
4006 on the left, 459 on the right... the grip frame looks thicker on the 459, but that's because the mag well on the 4006is beveled.
The Uncle Mike grips are out of print, but they are routinely seen on ebay at reasonable prices. They are rubber but don't have the sticky feeling like Hogue or Pach's.