The Mag5 has the same max head but a higher max flow, though it isn't any better than a Mag3 for our purposes. This graph should show why that is.
Danner's data does indicate better flow at very high pressures, 9' & 10', but I question its accuracy given the way it dips suddenly and comes back up. The example system is an estimate of Bill's test system given some information he posted in the DDC thread. Even if you had a really low resistance loop it wouldn't make any difference.