I now have a 5/4/3, and other than a rented 3mm and my shortie (and 7mm Farmer John a very long time ago), I can only offer a comparison of my 5/4/3 outcomes vs. 3mm outcomes in the same water.
A number of us have been doing shore dives in Ft. Lauderdale as of late. The water temps are around 70 degrees. I've readily noticed that during, or after, my dive friends are stating they are somewhere between cold and 'frozen,' where-as I have not yet been cold. I think my warmth must come from the Evo 5/4/3 suit because some of them are even wearing hoodies, while I do not. I do wear 5mm gloves and what seem to be thicker neoprene boots, plus currently use AquaLung Rocket II fins (which might be the whole reason I am warmer).