Hey Matt, from what i know, majority runners go for winstrol, however, test will also do a great job, even if its primary function is to build you up, it definitely will not slow you down.
i would avoid anything that attacks cardiovascular system stick with very clean products like inj Primobolan. HGH can be good too and obviously EPO but you need to be careful with EPO
Speed and stamina depend on your muscle fiber type not what steroids you take.leg speed is determined 6 weeks after conception and depends if you have predominately red muscle fiber or white muscle fiber. as red fiber is slow twitch and makes for more stamina like marathon runners and white fiber -fast twitch makes you more power based like sprinters.if your a white fiber muscle type then stamina will come from training and staying away from roids that effect your cardio ability if your a red muscle fiber type then speed will not improve only your technique to make u faster.