I'm not able to compare side by side. I'd need to measure to be sure, but it does look like it may have a little thicker top strap from the photos.
I don't know if the fixed sight channel was cast in or machined in on the fixed sight GP models. Wouldn't be too hard, I'd guess, to remove that channel from the lost wax casting process.
I have noticed that the scalloped frame fixed sight Six Series double actions have a thicker top strap - scallop allowed the weight to remain the same. That had to be a completely different mold, I'd guess.
Hope to see one of these competition models soon.
Terry T