If it stops for you while it upgrades itself (on 26%-27%). Then just kill wine and restart steam. Eventually it will restart itself and continue from point where it crashed.
That's a different bug...which, by the way was closed FIXED, and now I don't think it was FIXED anymore - I ran into the same problem recently. I am considering reopening it, but I will not do so, until it's consistently reproducible: http://bugs.winehq.org/show_bug.cgi?id=3084
The bug I am referring to, that prevents steam from running is: http://bugs.winehq.org/show_bug.cgi?id=3293