Thanks for all the replies and input. It sounds like all the GP100s are good quality. If anything, it seems that the newer ones might be a bit better.
This past Thursday, I had a chance to look at a pair of GP100s at a shop. Indeed, the stainless 6-incher I handled probably had the nicest fit/finish of any Ruger revolver I've seen. The blued one seemed fine, too, but it was not the sort of deep blue I'd like to see on a new revolver. Anyway, I almost bought the stainless, and I may yet go back to see if it's still in the case. The price tag was $599, which might be a bit much for me to absorb in the middle of the holidays.
It's clear, too, that the Six-series Rugers have quite a following. I have actually owned four separate ones over the years, but I've yet to find one with a really good trigger. I've really wanted the Sixes to work for me, but it seems to be a gun I simply can't shoot very well.
Finally, I actually like the full lug on the GP100. That GP100 with the 6-inch full-lug barrel felt RIGHT in my hand.