MR & TR blades are among the last places you'll get ice, because they're being warmed by moving through the air at very high speeds, sometimes near the speed of sound. Feel the blades sometime immediately after shutting down, and you'll find they're very warm. The extreme inboard portions, though, aren't moving that fast and can get ice.
As for what temperatures you can fly in with what equipment, that is in the limitations section of the RFM, or in your Ops Specs.