For speed, you'll need strength without size.
So you'll not have a huge choice : winstrol, anavar,halo (very toxic), maybe tren and prop (but at low doses). Deca can also help for your joints -track and field is very hard for joints- and Eq for stamina.
A classic stack for a speed athlete : deca/winstrol (deca for joints and recovery, winstrol for strength).