Download the .exe CO Timetable to your PC (found under Wireless Tools on co.com).
Pull up RDU-IAH on March 11th, and select "Requested Date Only."
Shows one 738 (6:00am), two E45's (8:36am and 11:34am), and two E70's (2:35pm and 5:30pm).
This doesn't help you buy them, but at least you'll know they exist so you can go hunting. It's definitely worth the effort to avoid the E45's.