I would follow the label for both produts. I've never used Stak, because I never really thought it was worth the money. I used Nolvadren-XT a few years back though, its a solid aimistane product. It did give me some sore elbows, which is common for me with arimistane. If you plan on stacking both, I would simply follow the labels. Nolvadren-XT will probably deliver the most benefit though