Thanks for the update. I will see if maybe this weekend I can send my P2500 into midi-ox to compare with your results. I might even try my emagic MT4 (little brother to one of your interfaces IIRC). I mention the MT4, because it's midi thruput is absolutely horrible--it couldn't even handle the after touch stream from a Casio DH-100!!!
I never measured BPM in midi-ox. Hope it's easy. If not, I will ask how you did it.