I've run both the 28's and 32's outdors and they seem to hold up similar to the RP's. For me, they seem to last a little longer before they start to get the stripe of death on the inside edge.
From what I'm seeing, you can run the 28's until the track gets up to about 110 degrees. After that 32's are the way to go. The 28's will grain up if you run them much above 110 degrees track temp.
We've been using oil based traction compound (tire tweak, corally, etc.) and letting them soak for about 15 to 20 minutes before the run. Haven't been using tire warmers.