With regard to cross-chaining, it's a matter of lateral chain movement. I can use every
combination on my 10 speed (2+5), because lateral travel is minimal compared say to
that of a 10 speed freewheel. I'm old; I use a 50/34 compact chainring. To compensate
for the big jump from 34 to 50, i put on a cranked down triple front derailleur which seems
to do a better job of picking up the chain.