Alright The Man, you wanna argue mechanics? You can easilly get Sabin hitting max damage with Bum Rush. You can easily get Terra hitting max with any spell in the game. The only thing that matters in a fight now is speed, which Sabin wins on.

And Terra, in terms of mechanics, cannot morph before a fight, not that it matters. In a mechanics argument, she can still hit for max. Once again, the fight hinges soley on who goes first. This is why a mechanics argument is dumb.

Dropping Mechanics, this depends solely on the rules of the cage match. If we go bob's no magic route, of course Sabin wins it hands down. With Magic, the confines of the Cage does lend it'self to Sabin. He is able to easily climb at high speeds, so I see him pulling a Vega and still being able to strike Terra mid-air without much hassle. Not to mention Aura Bolt and Windslash, possibly Fire Dance, all lend him to being able to fight her.

Again, being confined to a cage is at his advantage as Terra's Arial mobility is hindered do to space issues. Still though, Terra's magic prowess is intense, seemingly at full force she is able to level houses when unrestrained. (Of course, it's hard to tell if her power is as destructive when under control, as the game doesn't go into it. I would imagine the unrestrained and out of countrol might is stronger, as the game only really depicts Espers as really scary durring such a state.)

Sabin having martial training that seems far superior to Terra's means he's not likely to be missing much, if at all. Terra has excessive magical force behind her, and can pretty much carpet bomb the guy. In terms of damage output, I think Terra is shown to be higher, but at the same time Sabin's fortitude is intense, definately more so then Terra.

So, ignoring Mechanics and just focusing on the story and character, it comes down to who can withstand the punishment longer. So, in the confines of the cage, I give this one to Sabin.

Were the cage not a factor, however, I don't think it's much a contest, Terra would win it.