don't be so persimistic. O might just make it. I have 3' gar living with an O for ages already. I raised the aligator with O ... funnily enough i was afraid that O would devour the poor gar. I had an O being eaten by RTC though (but O was rather smallish)...
My three gars (3', 3' and 2') are living peacefully with two RTC (2.5' each).... two marble pims has been added to the fray (one was eaten by RTC), the other one had his whiskers cropped by some tank mate. O has been living with gar was ages
my experience of keeper aros with gar has been tragic for aro (as i mentioned before gar went over the divider to kill the aro ... both were still puny juveniles)
my friend's gar (now one of mine) has eaten an edli poly ... when they were both juvi
