Noam-

I would bet out. It is large pot, you have two strong overcards, it is a moderately coordinated flop (5 cards w/in rank of each other, but rainbow). You need to bet this to buy outs or win a free card on the turn. Yeah, because it was checked thru you'll get a free card anyway - but so does everyone else and now they have a chance to improve for free. You probably won't win this pot here against 5 opps but a bet will improve your chances to win later.

Why do you think someone has a pair? Someone could just have a 4x or a 5x, 98, or other weak draw. I could be missing something, but nothing here tells me someone has a pair.