ok, the thunderbolts speed demon (3drop) attacks my sabretooth-feral rage. since the attacker has priority, he pays 1 endurance to ready his speed deamon so he cant be stunned. it goes on the chain. I exhaust my sabretooth and play insignificant threat. it goes on the chain. since the last effect happens first wouldnt, I maintain that speed demon would get stunned before his unstunnable effect could take place. am I wrong?

You're totally correct. That's how the chain works. You get to respond to Speed Demon's payment power, and your effect resolves before he becomes unstunnable.

As long as speed demon's effect hasn't resolved yet, it should work just fine.

EDIT: Beaten!