a k high straight flush). so for any other straight flush, we're having only 46 choose 2 combinations of other cards we can select ( 1035 combinations per suit ). so if we're only interested about non-royal flushes, it's going to be 4140 * 9 = 37260 opportunities. when we divide it by total opportunities, it's 37260 / 133784560 , which is about 0.028%.
if we're including both straight flushes and royal flushes, we're getting any straight flush in about 0.03% of our random hands. so like about 1 in 3333 hands would be a straight flush, if every hand was played to the end.
in real life, it will depend on 