Everything I've read says the 2123 is a great driver and I'm still trying to get a pair, I just wanted to give you an FYI, about the slight differences between the two response curves. Close enough, but not identical. I'm still deciding on my midrange. If I can, I may just use a pair of 2123's in direct radiator mode. If I can't find any 2123's for a reasonable price, I'm considering Wayne's Delta midrange and Adrian Mack's Alpha midrange.
I've never seen any 2012's used either. They are 10 years old now, so you'd think some people would have extra, but maybe people really like them?
-Ian