Shipwrecked

[rikz]

I play a monthly "dealers choice" home game that starts out as a couple of hours of SSNLHE but ends up with a couple of more hours of games like "Low Chicago Follow the Queeen." Tonight, we had a new player announce "Shipwrecked" that had so many possible wild cards that we couldn't figure out if "5 of a kind" was more or less likely (and therefore deserving of a higher hand ranking) than a straight flush.

Sure enough, in the first hand we played, one player had a straight flush to the King and another had 5 sixes.

Based on the following rules, which hand deserves a higher ranking where the less likely hand is ranked higher.

(1) It is a 7 card stud game with an ante in which each player gets 2 hole cards and 1 door card followed by up cards on 4th, 5th, and 6th street, and the last card is down. There is a round of betting on each street.
(2) The lowest "down" card is wild for each player. So if player 1 has 2-K down and 7-7-2 up on fifth street, then he has four 7s. Meanwhile, if player 2 has 5-5 down and A-5-A up, then that player has 5 Aces.
(3) To avoid having the last card change your starting "wild" card, you can "buy" your last card "face up" for 1/2 the pot. Having a new wild card because the last face down card is lower than your previous lowest down card is to be "shipwrecked," hence the name.

So, while this is a silly game, I was wondering if anybody had any idea which hand, after all 7 cards are dealt, deserves a higher ranking based on their relative probability, a straight flush or 5 of a kind?

The one hand we played ended up with so much disagreement on whether a K-high straight flush beat 5 sixes or not that the players chopped the pot and we probably won't play that one any more.

Thanks.