I havent had IUI but I would think that the faster/slower stronger/weaker part would be negated by the fact that the sperm is put in much closer proximity to the egg and with optimal timing? So I would think that there wouldnt be any huge obvious bias? I would think that the father and his family history would play more of a role? Some families have a genetic bias to produce healthier boy or girl sperm and it can usually be seen by looking at the children that father has already produced, what his father and grandfather produced and also any full brothers