KK on a connected flop - what should I do?

[DVO]

I wonder if this is an easy decision for the vets around here.

2nd hand of the tourney, no read on anyone yet. $50 + 5 NL party SNG. Everyone still has ~ 1000 chips. Blinds 10/15.

I get KK in late position.

two limpers to me. I make my standard 4 X BB raise of 60. The blinds fold, the two limpers call.

3 to the flop:

7-8-9, rainbow.

To my mild surprise, EP bets out 100. To my greater surprise, MP guy then raises to 350.

I know my decision here is raise or fold.

Comments?