Rundown, exactly my feelings about Silverstone today - nothing learnt and no time to retest. I've looked up the leading women's times compared with their best from last year and 4 mins down seems to be average, at your sort of pace, so looks like you could have got your 71mins. As for me, BR, I wouldn't have been particlarly happy with 1:41, but bettter than 1:45. (and playing host at my aunt's 100th birthday party was more tiring than I would have like the day before a key race)
and BR, like Rundown and I have said, I don't think you can read anything into a race in as difficult weather as today, especially with your hamstring and calf problem as well. As for the HR to pace ratio, I think that is only valid in perfect weather - temperature and wind, and on a flat course. And I wondered what the effect of pain would be, when I had toothache last week.