Have you considered using a JBL 2020? It's a 12" driver that works very well in large format midrange horns, and would give you the performance you are hoping for. You could also use the 2012 or 2123 10" drivers for midrange applications; They're perfect in horns like you're planning to use. You might also check out the Eminence Delta 10 and Delta 12, which are other drivers that would probably work for you.I've been toying with midhorns using those drivers and I must say they're looking pretty good.