Juxt - Sorry, I hadn't realized you were racing too! No offense to
pbm since I think he's on a new level also, but I think you're on a different level than him too! Your training right now is boggling my mind. You've got more than 6:2x, IMO. Damn this is going to be a fun weekend!
Since we're all playing the guessing game right now, I'm going to say
pbm breaks 1:24 and
Juxt breaks 1:22. You guys have gotten so much faster than me, bastards.

I'll be betting both of you get your 2:59's (or better) this fall.
Hang10 - Sorry, I can't really say for certain other than taking a wild ### guess. All I can say for sure is 183 is probably not something you'd want to run for long during the marathon! From a pure numbers perspective, that's 90%mHR, so I'd guess it was closer to HMP than MP. I'd take a WAG and say 183 would be the very top HR I'd want to see on your watch in a marathon, with a 173-183 type of range being what I think you'd need to be in. You're training range is higher than I'd think too, so I could be way off.
FWIW, all of my HM's have been 91% and fulls have been 87%. The HRs been eerily consistent over the years for both distances.