[bigredlemon]

you are at least 80% to win it, and thus a 4-1 favourite.

the raise to 400 looks like he's saying he has a hand that can take the desperate small stack all in with; likely a middle pair.

Your re-re-raise screams a monster hand that wants to win it right there, likely QQ-KK and AK.

Calling would be very bad here because no one bluffs into a dry pot since the small stack will be going all in there. If you bet the big stack will fold unless he hits.

Raising to 750 would pot commit the big stack to call as a huge underdog.