I can't give you an exact number, but I'll get you close... I did 24-40 on 4 toons in just under 2 hours /played with recruit a friend there. I believe at the time it took ~45 minutes for me to do 5x runs and get locked out, this means ~13-14 clears of both Cathedral and Armory. You'll need 3 times as many without Recruit-A-Friend. So, around 40+/- clears should do it.

Unless having an L80 instead of a L70 booster affects the XP much, I don't think it does though.