I was pretty excited to try Mobil 1 Extended Performance 5w30 after a few runs of the "vanilla" version when I read on the Russian Oil Club website that the former had a slightly lower NOACK loss and was a little less viscous at extremely low temps.
However, I was really surprised to find myself hearing some slight rattles that I had never noticed before and that seemed to go away when I used something other than EP at the next change. They weren't super loud and generally seemed to be not long after startup at fairly moderate temperatures, but they did catch my ear and irritate me. Maybe there could have been something wrong with the particular Tokyo Roki filter I used from my stash for that change, and I do also notice that the viscosity of the EP product is ever so slightly lower at 40C than the standard 5W30. The EP also has a slightly lower HTHS, but this wasn't a full operating temp thing.
It was probably just some funky thing that had nothing to do with the EP, but I haven't used it since.