Couldnt the shearing be purely related to the wide spread ? Penrite who have a full sin range of PAO and Ester admit their 0w50, 5w60 and 10w70 will shear down, where as their Sin 15w40 and 25w60 are shear free. The last 2 mentioned may even have GP3 as they dont describe it in the same way as the PAO and ester Sin versions. Mobil 1 5w50 is also a great shearer, people use it as if it was a 5w40 oil.
Thanks guys.