I run an ecommerce site thats all https when I'm logged into the back end (which I am 90% of the time), although my customers see just http until they hit the cart. I frequently post links accidently to the https version of the page and see the same kind of movement in the serps as I would have if I'd posted the http version.
So - in my case, it don't matter, only the http version shows up in the serps.