No offense, but I just don't think it's a good idea to use energy drinks for working out. With all the caffeine and sugar in them, your heart gets racing and if you're already working out hard, your heart is going to get strained with all that work. Also caffeine narrows your blood vessels which raises your blood pressure and makes it even worse on your heart.
Of course, I am kind of biased because energy drinks make me flushed and I get palpitations and the shakes. It's not so bad if I need them to stay awake on a long car trip or a night shift. But I can only really drink about half of a sugar-free Red Bull (which I find tastes better than the regular one).