Best way to travel from Bern to Florence & back ...

Need some help deciding best way to travel from Bern to Florence .. in terms of cost/time & which train. I need to leave from Bern on July 23rd and head to Florence. My understanding is that Bern to Florence is 5.5 hours by train.

- Is best option to go from Bern to Florence? Or is there any scenic route that'll be more or less similar time/cost that I should consider.

- I'm planning to buy a 3 or 4 day swiss travel pass. 3 full days taking day trips from bern. Trying to decide whether it makes sense to use the 4th day for train ride from Zurich to Bern (day of arrival), or to cover part of the cost on 5th day leaving from Bern to Florence.

- Also - our flight is out of Zurich (could not get good flight for Italy) .. so i'm coming back to Zurich after 6 days in Italy. Should i consider any scenic route on way back? I read about bernina express - wanted to see if there is a way to do a shorter segment of that - which can fit into say 6 hours so ride.