I am with Michael R 1974 above.
I have done extensive testing of both using the wonderful Schliecher lens resolution chart, a Kodak 10 step grayscale card, a heavy tripod and very careful processing using a variety of developers and development times. In all cases Across was both finer grained and of higher resolution than Pan F 50. The only films I have tested which are sharper than Across 100 are document films and Agfa APX 25 ( of which I have a good stash). In pictorial work I have found Pan F to have somewhat punchier mid tones than Across and it is a very nice film, but unforgiving in exposure, so I shoot a lot more Across because of the extra speed and more generous exposure latitude. Just my 2 cents.