WSOP 2009 BEST DONK FOLD
This video sums up your dilemma very well.
The answer is basic.
You had two options play the KKs or fold and use the information you have gained from your opponents again in future hands.
Reading your post and before I got to your conclusion of you folding KKs I concluded that I would have played my KKs all the way.
With your description of UTG+1 pushing in his chips that is a classic sign that he is either bluffing or has a strong hand.
I would have called his 650 in your position.
You shouldn't have freaked out.
Yes, you played 3beated the KKs too weakly as psychologically speaking your 3 bet was too small as there others would have sent it as chunk change/you limping .
You should beat enough so they would have to think about it, I would say in the $55-$75 dollar range depending on the other players stack size compare to you. Logic behind this, is with the info you presented most people had roughly 500 chips average per person, so psychologically speaking they would have to think about if the really want to put in just over or under 10%of their chips. This also may help to disrupt the other players original betting plans.
People need to stop playing ABC poker regarding how much times the big blinds and need to be more creative with how much to put in.
Most players with medium pairs have this "tell" of pushing in really big to scare others away.
85, he was "trying" to be really creative, testing the waters as one does or a donk?
People tend to try and cover there tracks when they know they are beat eg, Tom Dwan.
When playing with new people I tend to match blow for blow to let them know that if they want my chips they have to work on it.
Me personally I would have called with KK in fear of someone holding AK and after the flop I would definitely would have pushed ALL IN.
I would have loved to play at your table, lots of chips of be gobbled up!!!
Final bit of my two cents.
After everyone called, I myself will be WTF? and wait for everyone else s actions, which I assume someone would have bet big or shoved all in? and I would have called or shoved all in to protect the trip Ks.
Reason for this is that the trip Ks will be a huge favorite to win the side pot(s) even if you don't win the original one with UTG+1, due to UTG+1 has already gone in and can't win the other side pots.
Using the winning side pots strategy is something I have not seen a lot of.