It probably depends on how much the standard fill, fills the chambers--loose fill will benefit more than packed fill. Bags with continuous baffles might benefit more from overfill than bags with smaller, divided baffles.

I could envision adding fill to my Ultralite because there's spare room to move down within the side baffles. I have an overfilled Dakota winter bag and it practically stands in the corner by itself. I never saw one with standard fill to compare.

Cheers,