Just curious, but why do you need such a slow film in sheets? The reason for tolerating a very slow film, for me, was to get very fine grain. I don't need that when a 16x20 is only a 4x enlargement. TMX has finer grain than Pan X did, not with the same look granted, but finer grain.
I was making some 11x14s the other night from 6x6 negs cropped to 6x4.5 or so to fit. You can only see any grain if you stick your nose right against them. I'm a severe myope so without my glasses I can do that. I dare so most people couldn't see it at all without a magnifier. That's over a 4x enlargement, and it's FP4+.
Maybe you print very, very large, say bigger than 20x24?
I like Pan F and shoot it in 120. I very much doubt I'd shoot it in 4x5 even if it were available.