If you're tacking this on to a work trip, I think two cities will be a lot. You lose most of the day to travel between them. I know it's a short train trip but switching hotels and all of that will eat up a lot of the day. Think about if you came to the US for a couple days and did 2 days in NY and then went to Boston for 2 days, how much of the time would be spent just dealing with the logistics.

I would do Florence for a week before I'd spend another day in Rome. But that's my preference. We did 5 days in Florence and 2 in Rome and it was plenty for me.

How is it budget wise between the two?