I have a really sad story re: your rule.
My ex and I adopted what we believed to be at least partially Maine my excellent compatriot (he was !@#$ing HUGE). He had been hit by a car and rescued. Although he was neutered, he was still extremely aggressive toward my ex, play clawing her (we refused to declaw, even though he was kept inside our apartment).
There were a couple of times where he just... looked all crazy and pounced/clawed my gf with both minor cuts and some deep gashes.
Fast foward a year later, one time, he was by the screen door where another cat was walking by outside. He's howling like crazy, and I'm trying to close the screen door so he doesn't claw it up. I try to pick him up, and I suppose he thought I was an enemy; he leaps onto my arm and digs the f--k in, leaving me with some small scars I still have.
Fast forward another year to 2010, my ex and I split up, and she takes the cat. She says he's been behaving crazy and ends up clawing the f--k out of her again.
She goes and gets stitches and ends up deciding to euthanize the cat (something I wanted to do long ago) a couple of months ago.
I'm not saying Maine Coons are bad cats by any means, but ours was probably crazy since he was hit by a car and left for dead, and possibly abused by a previous owner in his short, sub 5 year life span.
My rule of thumb is never get an animal you cant toss if it gets crazy. One of the reasons why you wont see me with a big dog. Which means I will never have a dog because the only dog that interests me is a German Shepherd or Great Dane.
Those savanah's from the pics looks like a rather large cat and may be a bit on the feral side.