Does this matter in certain applications or not really? Does the base oil have the same effects on frictional losses or how a bearing moves dependent on temperature, just like how thinner oils help with fuel economy?
Reason why I ask is that I was reading the data sheet for the grease I used in my bike's hubs - it's repackaged Nemco synthetic grease - NLGI 1.5 with an ISO 460 base oil. I've looked up a few other greases and while the NLGI grade might be the same, the base oil viscosities are different.