EPR according to Wikipedia has a higher working temperature then PVC. This could be neccessary as the cable could (will) get hot when its wound up on the drum. The flexibility is down to the individual diameters of the wire cores within the cable. Because of the way round cable is made, unreeling it and winding it up under its own weight can cause the cable to delelope a twist so it will not lie flat on the drum, the flat cable should be better at this. I would consult your cable supplier, for min. drum diam/max length of free cable. .
Frank