My experience shooting 12ga 3.5" 2oz #4's and 2oz #5's at 1200fps/mv VS 12ga 3.5" 2 1/8oz #5's and 2 1/8oz #4's at 1050fps/mv was the slower 2 1/8oz loads patterned consistently better and put although not a great deal more pellets in a 10" circle at 45 yards, but enough I would use them over the 2oz loads.
This was true for both my 870 Supermag and my Benelli SN
As a matter of fact I just ordered a bunch of 12ga 3.5" 2 1/8oz #5's WLBXR's I found on line in stock today.
Unfortunately I didn't save my targets. I remember being impressed that the 2 1/8oz #5 shot didn't just put more shots in the 10" circle they were noticeably more evenly distributed VS the 2oz #5's.