HEy Sidewinder,
I have complete confidence in your tackle's ability to bring down a buffalo, especially if you are using 800-900 grain arrows. You've just gotta make an accurate shot within a reasonable distance, and I believe that buffalo will be yours.
I have a copy of Traditional Bowhunter magazine that is several years old and in it is an article about women and traditional bows. In it are several women who shoot traditional bows that pull 45-48 pounds and they have killed deer and elk with them. They use reasonably heavy arrows, between 485-550 grains.
There is also a woman who hunted in Africa and used a 43-pound recurve to bring down a kudu bull. She was shooting 680 grain maple arrows and had complete pass-throughs on the largest animals (kudu and gemsbok). She took shots at 18 yards or less, but only if the angle was perfect.
If you have any doubts about what arrows are capable of, keep your eyes out for my article which should be coming out in the next issue or two of Primitive ARcher. It's titled "Putting Bird Points to the Test". I think ya'll will enjoy it.