Have you priced out individual tickets on the Deutsche Bahn site to assure that's the better value? I did Frankfurt-Dresden-Berlin-Hamburg-Mainz with individual tickets over 8 days and that was a far better value than buying a rail pass (saved about $100), though mine would have not been in first class. I have bought rail passes in the past but in recent years the individual tickets have seemed to be a better value, particularly if you can book a couple weeks out for the best fares.