Today's temps ranged from 33 to 28 Fahrenheit. Conditions were (are!) perfect for wet ice, and I was able take the StarGrips out to see how they perform in those conditions.
As you might expect, the tires are over matched by wet ice. Any deviation from flat ground, and the bike washes out from under you. Don't brake. Don't lean. There is just no grip to be had on pure ice when the temps are at the freezing point.
old ice, the white packed stuff you find on roadways, that the tires can handle. I'm also comfortable on some of the crusted over ice that I found this evening -- the crust on top offered enough friction to the tires. And on packed snow like we have in colder weather, the flat tread profile helps with stability and flotation.
For wet ice though, use studs.