Higher BB/higher CG is a bit of a religious issue. Personally I think I like the feel of a lower BB, 7.5 to 8 cm drop. But one of my best bikes ever, a 1980 Woodrup, had a 6.5 cm drop. It seemed a little toppley when I rode it, but it worked well on a long tour.

A 3 cm reduction in reach is rather drastic. Are you sure you didn't back up too far? Considering this your idea to just buy an arbitrarily shorter frame is a shot in the dark. Is there any way you can try out a friend's bike first?

Another consideration in shortening the TT is toe overlap. On your current bike, how far are you from toe overlapping the front wheel? It'll rarely happen at speed but it could happen at low speed when the bike is less stable. If you are not practiced in how to react, you may go down.

Then again, some people are never bothered if the toe interferes with the front wheel.

Ultimately, the requirement for frame sizing is that it must enable proper bicycle fitting - the actual placement of the contact points. It's preferred to have the correct fitting locations not at the extremes of the positions for bars and saddle that can be achieved with a given frame. I'd say that if you have confidence that these conditions are met with your new frame and cannot be met with your old frame, then go for the new one and see what happens.