Chinese cuts don't correspond to American, French or British cuts, so it's difficult for me to say. In fact, Chinese cuts don't correspond with those of the the next butcher along. It all seems very random.
For stir fried dishes, which I make often, I tend to mainly select beef with a clearly visible grain. Certainly, sirloin works. Flank is known as skirt steak in the UK, but I've never used that for stir fries, so cannot comment.
Marinades tend to be used more for flavour rather than to tenderise. They usually consist of soy sauce and rice wine.
2 hours ago, lindag said:
1 cup soy sauce, low-sodium soy sauce
6 tablespoons sherry or cooking sherry
2 tablespoons cornstarch
4 tablespoons brown sugar
1 tablespoon ginger, peeled and minced fresh
That is a huge amount of marinade (and a humongous amount of sugar). You could do a whole cow with that! Ingredients for Chinese stir fries tend to be measured in teaspoons.