First off, just got back from diving in the caymans, and I saw one of these golden groupers, and I must say absolutly an amazing fish. It was maybe 7" long and it swam right up to my mask, then darted back into a crevice. Beautiful fish.
As for size, majority of groupers pass up about a foot and a half no problem, with a few exceptions... I would imagine it would be ok in your 300 for more than a year however. Grouperhead will chime in on that, he's the expert. If you get it, make sure you have somewhere you can take it if it gets too big, for instance a LFS with a huge tank.
As for the saddle back, I have one in a 125 and its growing pretty quickly. Im going to have to move it in a year or less.
