Some time ago one of the clean-hands car rags (C & D, I think) did a comparison of 15's, 16's, 17's, 18's and maybe 19's or 20's using one vehicle. The test involved a series of traction (both acceleration and braking), handling and ride quality evaluations on the same car on the same road surfaces. Not surprisingly, 17's were found to perform best overall.
The car originally pictured in this thread looks pretty good in my opinion, and I generally don't dig wheels bigger than 18" unless the car is designed around them (ie Corvette, SRT-8, etc). Usually, 20x8's or 20x9's look too tall and narrow for a G-body. I also agree with the comment that the stock brakes become dangerously inadequate when used with such large diameter wheels, not to mention how small stock discs look and and how ridiculous drums look behind these big wheels.
I don't think I'd ever put 19's or 20's on something we build, so I guess I am stuck in the 80's with the other guys. My current car has 17's, so at least I'm in the late 80's.