@cardassianvole I would probably go with option 2 unless there's a substantial price difference, but I try to build extra time into my travel plans for exactly this sort of layover.
The last time I flew out of Heathrow I was heading toward the security area and as I was about to get into the line a security guy called me over, asked if I was an American, and then let me just bypass all the gate security, but I was hitting the gate at a slow time so I wouldn't count on that.
@neal Yeah, I am probably going with that option if only because I don't want to be stressed about it. It has taken me 90-120 minutes to clear customs at LHR before.