Hmm, well street level speed is typically of low quality. I have no experience with these these tablets therefor little insight, still, I would take no more than half a tablet for your first dose, preferably 1/3rd just to see what your dealing with here. Whatever you do start low and work up, you can always take more if your not satisfied. Hopefully somebody else has experience with these pills and could help you out. Please, do be careful though...