The elastomers just get harder and harder (or slower to compress?) with lower temperature. That's one of the reasons why in cold climate countries winter tires on cars are basically mandatory. It would be interesting to know, if with lower temperatures the elastomers become slower or harder or both.
The rebound rate an Elastomere has is the same as his compression rate. Up to a point, that is.
I agree on the progressiveness. There are progressive steel springs though. And you can mix a non progressive steel spring with a short rubber end to gain a little bit of "progressiveness" on bottom out. In fact it's something you should do.