Chorus 10sp is very nice, and I like it a lot. That being said, the biggest bang for the buck in the earlier 10sp groups is Centaur, in my opinion.

You'll be hard pressed to feel a difference between Centaur and Chorus, and you'll save a bunch of dough going with Centaur.

I agree about keeping the vintage seat post and headset, but you'll really be missing out on a significant performance enhancement if you don't use the more modern brake calipers.