Mark -The Fuji 6X9 RF's are even easier for me to handhold than my Nikon, though I shoot on tripod whenever possible. So I generally load them with TMX100 instead of TMY400. Either speed will render a very nice 16X20 print, but the grain will be almost invisible with the 100 speed version. Pan F has a different look - more a blended "watercolor grain" effect, yet with excellent edge acutance. TMax 100 is capable of extreme detail, but need a little more grain growth than PMK pyro supplies, so I use a different developer for it. I've only seen pictures and travel documentaries of Wales and Scotland; but much of that, and also the coast of Ireland resembles our Marin County right across the Bay. Pt. Reyes Natl Seashore is the second foggiest place in the US; but all that fog reaches my place here along the Bay, and all the wind too. It's rare for a midsummer day to get above 60F. But just 15 miles inland, behind the first range of hills, it can be 50 degrees F hotter in summer. It's all about microclimates.
Augustus - I'm not a film chemist, but I certainly understand that grain growth options have come a long ways, and your blanket generalization of it simplistic at best. T-grain technology, for example, allowed for more lumen capture area at smaller and more consistent grain size, although the early version of 400 TMax could be a little bit clumpy. Efke 25 was even a little slower than Pan F, but not only had far greater dynamic range, but even greater detail capacity. In that case, by limiting the red sensitiivity, and going orthopan, they minimized the light scatter somewhat. Too bad their anti-halation layer wasn't very good - had to be very careful loading those rolls in the shade.