Gazelle Special

Cassettes with greater difference between the smallest and largest cogs?

Yes, search in the Campag catalogs onm the Campagnolo site for what cassettes what mechs are recommended..

EDIT: I also found people noting that the rear derailleur is for triple. Will those be compatible with double groups, because I can imagine the rear derailleur needs to adjust to what happens at the front, but does this make a big difference?

Triple mechs are most probably long cage, but my triple 10sp group is with a medium mech.. That was with a 12-23 cassette, I hope it'll work with a 12-25.. Long mech would work for a 27plus rear cassette with a double (compact) front in my experience..