Given that a mile is too short a distance to check splits/make sense of HR data, etc, IMO the easiest way to think about it in terms of pacing is in relation to your interval training. Depending on rest period, number of reps, etc. something like kind of speed you hit when doing 400s is probably in the right sort of area.
Those figures above make sense to me; I think there are two reasons why the McMillan predictor may be a little bit ambitious. Firstly, presumably you're not specifically trained for racing over this distance, so you may struggle to convert your 5k time downwards. Secondly, (I'm fairly sure) McMillan changed its formula at some point, making shorter predictors even harder to hit. Maybe you're best off going out at something like 4.00m/km and trying to hold on as best you can. If you feel comfortable for most of the race with a fresh kick at the end, you haven't tried hard enough!
