I'm using my current horns in a three way system, so a 300hz horn is preferable. In fact since I'm using a steep 24db/oct x-over I'm pushing my current horns MR-64 to 400hz. This is for home use of course and while not optimal, it sounds better to me than using a 500hz x-over. My somewhat crude RTA analysis doesn't show I'm down any at 400hz either. I know at some point I should measure my bass horn and mid range horn (outside) and then come up with a proper crossover slope based on that.
Funnily enough I've often wished for a 300hz horn since that 288 driver sounds so nice I like to use it as low as practical.
I'll post back in the next 3-4 weeks once I've got these babies up and running.