I am not very experienced... but here goes what I have tested in 120.

T-max 400 in Rodinal 1:50 has non-perceivable grain in a 16x16 inch enlargement (about 7.5x) as seen from 1 foot.
It is less grainy (a lot less) than a Tri-X at 10 to 12 inch side print (4.5x to 5.5x), from Rodinal 1:50 development.
It was immediately apparent that the grain structure was not the same.

Depending on your enlargement sizes, T-max 400 might be the only film you will ever need. It is also one of the cheapest 400 films in Europe, if not the cheapest.