5K: how much should I have to beat my wife by for it to be fair?

Well. You are presumably male and so should be able to run faster than your wife…other things being equal. You are trying to compare PBs right?

Assuming that you are both 40 years old then a comparable performance for you both would show about a 3 min to 3 min 30 secs time difference. This is arrived at by looking at age graded performances.

I was surprised it was so much. It also makes you think how really annoying it must be for women who go running with their partners and their partners are a few metres ahead urging them to do better when actually the partners should be way ahead to be equally as tired (I over-simplify, I know).