With my experience, a Gato sub will go to crap at
precisely 597 feet. That's why i always try not to go below 550. But even then that's in the most extreme situation; i usually don't go under 400-450.
But a have a Balao now.... it rocks.

but the thing is after i get to 700+ feet i can almost never come up. i just keep falling like a rock until the sub levels out at 800... at 803 i'm heading to Davy Jones' locker