Let me preface by remarks by saying I've only used a Beseler 23C III and 45mxt (not the latest iteration).
The Beseler 45 is a rock solid piece of machinery that works for everything up to 4x5. The other thing is it is American and still manufactured. The 23C is also American and still manufactured. As was mentioned the 23C covers most of the normal medium format sizes. With that duo you can enlarge just about anything you will ever shoot. It is nice to have different enlargers set up for different formats. If someone was in Europe I would recommend a European model that had plenty of parts in the used market over there.
The Durst might be worth keeping if you really plan on doing color in the future. Depending on your geographic region enlargers and enlarger accessories can go for next to nothing. But the problem I have found is sometimes the thing you need for whatever reason just doesn't pop up when you need it. You already have a color setup. Unless you can get a good price for it or swap it for the same price as a Beseler color head I would be reluctant to let it go.
If I were you I would research what makes a good enlarger. One thing you seem to be overlooking is how solid the support column(s) is. The Beselar 45 is solid. The Beseler 23C is pretty respectable. It is the choice for many institutions. I don't see the Beseler 67CP being in the same league.