Beef Stroganoff is a Russian dish and I'll be the first to admit to know nothing about Russian cuisine or whether my version is authentic.  Probably isn't?  I use flank steak in mine which deviates from the sirloin, tenderloin or chuck I typically see in recipes. After having tried all of those cuts for Stroganoff at some point in the past, I stand by flank steak as the ideal cut to use in this recipe.  When sliced uber thin, the melt-in-your-mouth flank pieces are at harmony with the sauteed soft mushrooms and tender egg noodles.