Gilitar,
It is probably fine to try ... but watch for shearing. Like Shannow states, the wide-speard multi-vis oils are prone to shearing in severe conditions, even the newer ones which are much better than they were in the 80s and even 90s.
I'm kinda interested to hear why you are so interested in a wide-spread oil in Mobile, AL. Are cold starts really an issue for you guys? I'd run a HDEO 15W40 unless I felt it wasn't performing well for one reason or another. They are cheap, plentiful proven performers.