Oh hey, that's actually pretty useful! Thanks Sage.
Only ones that I think matter are Quez, Shiva, and Leviathan for me. I can't think of any even -tenuous- plot claims for the other GFs. Thinking I allow the skills from the GFs, so Squall gets Doom and (zOMG!) Card while Rinoa gets Recover; but no to junctioning stats. They can, of course, -summon- the GFs for some slow damage (better than their physicals!), and this is a bit more reliable for first-turn damage for those two than starting in the Limit range thanks to the random nature of their Limits. Also means they don't have to start in the OHKO range like Zell et all for damage.