1st class on the Rome - Florence - Milan Intercity trains is 1x2 vs 2x2 in 2nd - not sure about the room between rows - but it cant be too much worse than 1st as 1st is pretty bad.

Don't just European trains by Trentitalia - Trentitalia trains are dirty, there dont seem to be English announcements and they are usually too hot or too cold. I travel from time to time by train in Switzerland and France where the trains are quite good - Trentitalia is like the NY subway in comparison