[disjunction]

Yeah why not. Keep in mind that I did this quick and also I'm a certified moron (you have to apply in the mail).

47 cards out.

30 cards, 63.8% lose you 1 SB. 3 cards, 6.4%, gain you (estimated) 12.5 SB. 8 cards, 17%, lead to backdoor flush, I did more math and got a gain of 1.6 SB. The 6 remaining backdoor str8 cards I assigned -.45 EV. I weighted things by multiplying (percent)x(EV), and got:

-.638
+.8
+.27
-.45

= -.02 EV

What you get is roughly a wash. This is where some people tell me that I didn't consider if you hit but then he rivers you, as well as some other low probability stuff, but I'm offsetting this by the times your ace-high is best and you outplay him, which is kind of the reason stoxtrader was giving.