Larger Negatives imply longer focal length lenses which imply stopping down more to achieve depth of field, particularly where camera movements aren't feasible.

If this describes your proposed use of the 8x10 (else maybe you don't like depth of field?), then slower emulsions implies more reciprocity failure compared to faster films and longer exposure times compared with faster films. If you're outdoors, then this means more potential wind movement. Indoors it just means your shutter is open a longer time, and if you are using lighting -- just more sequential flashes to build up the exposure even for fill flash.

So, many using ULF prefer higher speed films over slower speed films. (You'll see this in both Dick Arentz's Platinum books as well as Dick Sullivan's book for platinum where they discuss film availability for larger formats). YMMV.

John Sexton's testing on TMX and TMY shows TMX has the best **(eg least) reciprocity failure characteristics, but unfortunately since late 2002/early 2003 they have included a UV filter layer in TMX which causes extremely long printing times for those using alt processes. this leaves TMY as the next best choice (far better than HP5) for reciprocity as well as having a high ISO speed compared with FP4 and others. << ** I've seen other peoples published reciprocity charts showing TMY is slightly better than TMX. John's results showed much better for TMY than TMX. You'll have to do your own testing>>

I use tmany (not Efke nor Bergger) - have a freezer filled with TriX, TMY, HP5 and FP4 in 7x17 and 12x20. I have noticed that older HP5, even frozen, tends to fog compared to Trix or TMY. My preferences are for Tri-X followed by TMY followed by FP4.....