I haven't used Alpine so I can't comment on it.....
However I did use Sweetex a few years back (when I worked in a bakery in Chicago). Chicago summers can be pretty warm and although we had nice air conditioning in the bakery, it could get a tiny bit warm while decorating too. We could make a 10 gallon batch of IMBC and the heat/humidity didn't seem to touch it. However my warm hands do!

As I mentioned in another thread, I would keep two bags going to try to keep from melting it.
The recipe we used was 4 lbs of Sweetex to 16 lbs of butter in the winter and 18 lbs of butter in the summer. That seemed a little backwards to me, thinking that a higher ratio of Sweetex would hold up better in the summer, but I didn't question it too hard. We'd keep the cakes refrigerated up until delivery, and try to deliver within 30 minutes to an hour of the reception starting. That would give the buttercream enough time to soften up. I don't recall management ever getting a call that the buttercream melted.
I don't work in a bakery anymore and don't really have a local supply shop to get small quantities from, so I'm *really* looking forward to my baking mistress having 3-5 lb sizes soon! (hint, hint)
