[SimonAllan]

I'm not saying that I would raise, but I think you can argue that it's a reasonable move. If you call 5th, you'll probably call 6th, and the river with any improvement (most likely to kings up). If you raise 5th, which is likely to eliminate most of the field, you may well get to check behind on sixth (unless you catch a jack or king), so going to showdown would be no more expensive than in the call/call/call line.

I just don't like the passive line, given that you are more likely to make kings up than trip kings or the straight, and kings up is very often a second-best hand in this sort of pot, whether seat 2 has trips or not.