Yes, I beat them. Emerald Weapon and Ruby Weapon. They both have 1 million HP. Those were fun fights.
But yes, there is quite a prize. Master Magic, Master Command, and Master Summon. One green, one yellow, and one red materia ball. Each one gives you every spell, command, or summon that can be gotten with that color. So naturally, I went into the Northern Cave, got a rubber band, and got them up to Master level overnight, so I've got three of each.
For the record I am the FF7 king. I've beaten it about 8 times (invested about 50 hours into 5 of them, 80 into the other 3), and my pride and joy is a save where my party (Cloud, Red XIII and Yuffie) are at 9999HP and 999MP at Lvl. 99, I've gotten everything in the game, gotten all the materia, done ALL the extra stuff, AND have fux0red the game's clock, which is stuck at 99:59:59. Booyah. I've memorized the damn game practically, and I still love it.