Stephen, thanks, I think.
As to low heart rate training, if you want to do it (and I'm not saying you should), you have to be patient, there is no quick payoff. My splits the first time I did 10 miles at low heart rate were 14:02, 14:45, 15:09, 16:38, 14:57, 15:37, 15:59, 15:43, 17:00 and 16:32. That's no kidding, and that's when I started running in the dark.
I think you will get a slower time in Park City, compared to the other choices. It is a specialty marathon for people who are trying to do a lot of them or otherwise not trying to get their best time. Pretty and challenging, but you won't be as fast there. As to the others, up to you, there aren't a lot of choices in Utah. (Did you check out the Utah Valley Marathon? I have heard some good things about that one.) I still think you should be in our St. George group. That is the fastest and funnest marathon in Utah, and we can still make conference for the afternoon and evening sessions, at least we did last year. It would be fun to have a lot of Boston qualifiers in the same race from the same family.
Here's how you beat me: Buy two old beater cars, $100 each (I didn't say it was free), stage a car wreck at mile 6 of London's Run, about 45 minutes after the starting gun, and hire somebody to sit on the side of the road with fake blood on his face, asking for a lawyer instead of a doctor (another $25 bucks). You'll never see me after that.
I love how the competitive juices are starting to flow for this race. Somebody is going to get hurt. Good stuff.