Not only is it quite smooth, it revs much more easily. A bit more power. I'll look at the mpg over the next few weeks. I did not have M1 in the car before. No complaints. With GC and winter 89-91RON gas, it was settling at about 30 mpg. I have equal amounts of Mobil 1 (0w-30) and GC stashed, all in all, Mobil 1 is better for me and I would use it preferably.
Likely I will keep using GC in summer to use it up. imo, I think GC offers a hair longer oci, but since I have an existing stash, extending past 3 months 8000 miles is pointless.