How long is a piece of string? I like Ilford FP4+ in Ilford ID-11 1:3. ID-11 is a good, all-round developer, my results are plenty sharp and detailed with unobtrusive grain. Mind you, I don't make 40" prints. Ilford Perceptol is supposed to give fine grain at the expense of film speed, though i can't quantify that. PAN F+ is a fine grain 50 ISO/ASA emulsion; I should think Pan F+ in Perceptol would give a very fine grain result, but I've never tried it. YMMV, of course.

BTW, I see no grain in your example image, but then it's not a 40" print.

Cheers,
kevs