Let's take a look at that Straight Flush:
You hold 567:
Okay, so you can get 34, 48, or 89 to pick up the straight flush.
There are 47*46 = 2,162 combinations of cards and three of those combinations deliver you a straight flush:
2162/3 = 1 in 720.67
The 1,081 you're thinking of is probably a straight flush draw with one of the cards being a gutshot, that would only give you two combinations.
Of course, even in the example hand, Qh, 9d, 4s, 6s, 7s, the 467SSS is still the better hold. 568SSS is closer (but still better) though closer because the 9 becomes a penalty card against a regular straight.