To put it shortly, it's not as bad as the nay-sayers think but also not as good as the weed-smokers think. I'm just a hobbyjogger and i smoke before almost every run because i enjoy it but I know if i wanted to get really serious that quitting would help. Make no mistake, smoking weed offers no physical edge. If you feel that it helps put you in the right mindstate or whatever then that speaks to the issues with your sober mind not to the benefits of smoking weed.
Do you have specific strains you smoke before a run? I'm going to have to try it with the Chocolope, a sativa, I have left.