I'm embarrassed I don't know this, but what part of the cow is Ball Tip? Some people tell me it is sirloin, and some say round. Also, what is the difference between "two-up" and "two down"? I've cooked using various cuts for years, but this is the first time I have ever been in the position of having to make the purchasing decisions, and sometimes I don't know what the terms mean. My sales reps are generally of very little help. Thanks!