I have these on the rear and they are fine and they are fine I used them on track last Saturday at Oulton Park and I can vouch that they dont warp because there is not so much pressure on the rear caliper as most of the braking is done at the front. I can also tell you as my car is a facelift that my brake bias at the rear is heavier as the bias adjuster has been removed(under the driver side arch) to compensate for the rear adjustable camber arms.
The problem I am having at the moment is it eats the rear pads when on track.. I will be looking to rectify this asap .
In short these disks are fine but I would be looking at oem fronts for piece of mind.