My first ST1300 had Bridgestone Exedra Radials in the original sizes. These were recommended & chosen for their durability while riding fully loaded and towing a trailer around Australia. After 15,000km of touring, the front was hardly showing any signs of wear, but the rear was replaced in Perth, as it wouldn't have made it much further than about 10,000km.
The Exedras endured some extended high speed running between Tennant Creek and Pine Creek, as we were following our Police escort vehicles at 130kph for most of that section.
The replacement ST1300 came with a set of partly worn PR3s. They went well in the rain on the Gillies Highway and have been quite OK in the dry around town. I intend to replace them with PR4 GTs. Having a second rear wheel with an Exedra on it for the camping trips towing the trailer, might even be a way to maximise the use of the PR4s, if they wear out much faster than the Exedra.
NOTE: The rear tyre profile wasn't quite as bad as the picture, while it was still fitted to the wheel and fully inflated.