Greg,
I'm sure you know you can just download C1 DB 4.5 and compare it for yourself but I think for existing backs, using V3.7.8 or 9 should be as good and more stable than 4.5. In fact, if you go to Phaseone user forum, you will see quite a few posts asking to bring back certain features that were on V 3.7.x
Good luck.