Adding some info 4 years later.
There is one downside to the #71, namely that you can only get blades that fit from Aloris. The #71 blade for AXA, BXA and CXA is 1.5" tall and available for GTN 2, 4.8, and 6. The #71 blade for CA and DA is 2" tall and available for GTN 4.8 and 6.
The #77 takes industry standard SGIH blades: SGIH-19 for AXA, SGIH-26 for BXA and CXA, SGIH-32 for CA and DA. These are approx 3/4", 1" and 1-1/4" tall, and typically available for GTN 2 and 3, GTN 2,3 and 5, and GTN 3, 5 and 6, respectively. Other configurations may also be available.
If you don't consider cutoff blades expendable, this probably won't bother you. We put a BXA #71 in a student lab, and they not only shatter the GTN-3 inserts in ways I've never seen before, they managed to mangle one end of the blade. At $90 each for a #71 blade, we might have been better off with a #77 and less expensive replacement blades.