Steroids are usually used to build mass. Doing marathon's and training for marathons wreak havoc on your muscle tissue. Exxtended running literally eats away your muscle. Running 25 miles a week wil rape your lower body mass, and also decrease upper body strength.
I would investigate all steroids, and focus on the ones that increase your red blood cell count while giving minimal if any water retention. That's what you need fo rrunning.
Aso, you need to decided if lifting or running is more important. It is pretty clear you really like running, so stick with it. And, in that case, you do not need to take steroids for marathon running my man. Weight holds you back, and steroids promote weight gain.
basically .. u need cals/protein cals to build muscle.. excess running is going to burn a shyt load of what u need .. do the math