I'm no battery techie, but I'll chime in. The King Kong 26650's have been tested to about 4,500mAh. The Trustfire Flame 26650 ("5000mAh" has been tested to about 4,300mAh). Those Keygos were tested to 2,951mAh.
EDIT: A good reference is the "26650 Batteries" thread. See the first post.
-Garry