Hi Smithy,
Running at Silverstone was restricted due to fog so I didnt get chance to give the R4 rears a proper test, however from what i have seen the R4S seem more suited to the rears, the R4 maybe a touch hard, braking doesnt seem quite as good but that could be many factors including a recent fluid change (even to the same fluid that I used before)
R4S rear still get my vote as the best yet in all Situations, cost/wear rate.
R4S / R4 fronts are also great very similar performance to Ferado but cheaper.