Tmax gets the straightest curve with TMRS developer. But TMX can shoulder off if overexposed in full range lighting; and that's a reason it should not be rated below box speed with certain common developers. Some developers will create an upswept curve at the top with TMY, but you've really got to
be up there where you don't belong to begin with. I've used a variety of developers with these films, but never XTol - and if Xtol does in fact predictably produce a toe like that, I wouldn't even want to
bother with it.