The corn we were in during that demo was around 21%M so header loss was not really a factor. The only differences we noticed in the heads was how clean they picked.
Although I did do a comparrison of my neighbors drago to my geringhoff last year in dry corn. It was not in the same field so I don't put much stock in it... but the corn was running around 16-17% in both fields. I thought the drago was doing a little better job with less butt shelling... but without running them side by side I can't say for sure.
Don't get me wrong here... I haven't ridden in the combine with you, but if you can get a 2577 to do what you say, I think I should have traded my 7120 for a 5088.
6mph in 220bpa corn with an 8 row head is about 3200bph... thats a repectable number for a class 7 machine... let alone a class 5.
But any time I hear people say the combine has no loss, I urge them to look a bit harder. Its impossible to set a combine for zero loss.
I have some 2' x 5' frames with screen door material between it that I toss on the ground under the combine and catch the losses... this is really the only way to accurately measure losses. I do it both spreading the residue and windrowing it. When I spread it I use 1.8 kernals per sq ft as 1 bpa loss. When I windrow it i go by the charts depending on how wide the head is.
All in all my point is make sure you accurately measure your losses and do it frequently. That will really give you a good feel for what you and your machine are capable of.
I don't care what brand of combine it is... if you know how to run it and are satisfied with the job its doing then you are "Winning!" as Charlie Sheen would say.