IIRC, we build Centaur-B in 1.75y and Rennie in 2.25y (Sol) or 2.25 and 3 elsewhere, so going for the C-B plans in the worst case will also save half a year of berth time. Or alternately we value an amortized rate, with continuous production they end up with about equal SR cost, the Centaur saves crew significantly, and we get almost 1.3 Centaurs for every Rennie.
Now, amortizing isn't necessarily relevant as build schedules usually don't plan around continuous production, but it is one way to calculate the value of berth time.
Personally, I'd almost favor a middle of the road plan. While we do need to close the cruiser gap (hah) we also do need more capable multuroles. The Centaur is currently pulling something like triple duty: scouting, skirmish, and covering sectors when more capable ships are drawn on elsewhere. Even with the deployment of the Kepler class we're looking at 5+ years until we get those duties covered in numbers. In comparison the Rennie is only really lacking for vanguard, its sector response duties are covered for by other classes including the Constitution and Constellation and Centaur, and the Miranda is a complement to it in fighting, being used for little else.
What I'm saying is a split would be fantastic. I think we need both these things.