I can only speak to the FirenzeCard, not having used the Roma Card. I have to agree with everything erodgreg says in the comments above, and in fact we were also in Florence last November, probably skipping the same short lines :). No need to purchase ahead of time, the pass is sold at some of the museums; we purchased ours at the first stop, The Bargello. We've been to the Bargello several times at different times of the year, and never a line, so there's an idea. I would suggest looking at the FirenzeCard website and coming up with some sort of a game plan, (because you can't see it all) and noting the hours for the days you'll be there. Using the Bargello as an example again, we love it, but it does have some wacky hours. Lastly, I highly suggest the Museo degli Innocenti and if you time it just right you can watch the sun set from the roof top café afterward. Bon Voyage!