[ilya]

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Of course I don't want him to call with a hand like 55 or KQ!!!! What crazy universe of sit and go playing have I entered? You want to be called by a hand that is either 40%-55% against you when there are already 700 chips in the pot, just to win an extra 600?

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Obviously you don't want to get called by 55. It's a disaster. Getting called by KQo preflop would be a lesser disaster at the worst as it is +$EV to call there preflop if he shows you KQo, but stop-and-go may give a higher $EV. I don't think he's folding KQ on the flop though, at least not unless you would have had him beat.
But I think you're right that a stop-and-go is better, as it gives pretty much the same $EV against hands like KQ and 55, but increases your $EV a bunch against hands like K8s.