FWIW, I fell for doing the update and now my Sigma 50 autofocus is abysmal. It was working fine before but is now completely useless. And of course there is no way to roll back the firmware update...
[EDIT] I found a copy of the v1.0.7 firmware and was in fact able to roll back to it and the autofocus on the Sigma 50 seems to be fixed. I'll retest v1.0.8 and post later with results of a more definitive test...