The advice given elsewhere on this board has been that you're unlikely to be able to convince a US institution to hire you with tenure coming from the UK as a lecturer, but instead need already to be at SL. So, are you interested in going pre-tenure?
Given some of the insane tenure decisions I've seen even at good US institutions, I think I stick with the idiot UK dean. Better an idiot UK dean that won't promote you (but can't fire you) than an idiot US one... Of course, if you get an offer to go with tenure, then all bets are off.
Just to add a note here about tenure in the US. It's extremely difficult for even someone at the SL/Associate Professor rank to move WITH tenure. They may put you on a 'fast track' to tenure at your new place... 1-2 years... which in effect serve as your probationary period, but they don't really want to get 'stuck' if you suck.