there's a lot of reason to run multiple compounds at one time because a lot of them have secondary effect. anadrol, tren, masteron, EQ, 1-test, deca, d-bol, etc...
there's a reason to run all of them in a stack and it really doesn't matter if you are running 4 grams of gear and hitting androgen receptor saturation, what kind of gear you're running is pretty irrelevant at that point with regard to gains.