I don't have data per say, but I am not sure if I can jump on the wagon that lump does not burn long. It can burn hotter, no question. Charcoal and lump, follow the apples and oranges philosophy, by that I mean, lump has twice the btu rating, of the same amount of charcoal, in weight. I have used lump exclusively for about 2 years now. Like you suggest, there can be a huge difference in suppliers, and a difference within a supplier over time. I have recently started using the Maple Leaf hardwood, out of Canada. Very good consistency, well packaged, and very little fines.
This past Friday, when I cooked butts, I 90% loaded the ring with a freshly opened bag. Lit about a half chimney full of lump and put it in the remaining 10% space left in the ring. My bottom vents were opened about 1/4" open. This kept my top grate temperature at 230 or so for about 7 hours. I pulled the barrel off of the bottom section, and then placed enough lump on to refill the ring. This was enough to finish my cook. Total time of 15 hours.
The key here is, you can introduce very little air with lump, and keep it burning cleanly, and maintain low temperatures.
I just went and weighed the bag, that I opened on Friday. I used a total of 8 lbs. of fuel for the entire cook.
Like I mentioned up top, regarding different brands, I have not had the same success with other manufacturers.
Size uniformity is a big factor, as you suggest, but I have heard that some people go as far, to take the larger pieces and chop them up a bit smaller, to keep things consistent.
Personally, I think that many people on this list do not use lump, simply because it is not very accessible to them, but I could be wrong. I like you wish there was more people talking about lump here.
Jim