I use Sul-Po-Mag which is the same thing- sulfate of potash 0-0-21 + Mg. I use it mainly because my soil is so deficient in potassium. There's no way to know if it helps with cold. Too many variables. IMHO the main thing that helped with cold is the fact that the cold spell came so late in the winter after the plants had been hardened by a number of nights in the low 40's, and even one night in high 30's. Also, the longer days now and the quick warm up has got to be a big factor. We only got down to 35 too. A few of my crotons have been down to 27-28 in 2010, which is wayyyyy colder as far as plant survival goes. I'm seeing some yellowing in some philodendrons mainly, but no losses.
It's still early, but so far I'm seeing just a few leaves dropping on a few cultivars. Very few. Interesting that it's different ones every year it seems. Maybe some things we don't know weaken one over the other each year. Who knows. I'm always learning something.