The numbers are pretty dramatic. Years ago I took apart an LS1 and a LT1 and measured the actual flow area.
A 3" LT1 had 60something% of a 3" pipe, and the 3.5" sensor has 80something% of a 3" pipe.
The other advantage is running a filter with a larger outlet neck. Even better if you put a 4" filter on there and squish it down so that you have a slight 'velocity stack' at the entrance.
Moral of the story, is ''it depends''. If your engine isn't taxing the smaller MAF, going bigger won't do that much. If you are borderline with the 3.5", then tossing the 3" and moving up will give large gains.