I will say that the shore rating isn’t everything like gear oil has a higher hardness rating (shore) than ultra grey, but binds nicer imo. The gear oil has a higher elongation % (200) vs the ultra grey (120) and I think that is the difference I notice in the bind feel.
Basically, I noticed that the ultra grey would sometimes spin out a bit as the yoyo returned, so the yoyo would return to hand, but be loosely wound. It feels like the gear oil grips the string better, so that once a bind does initiate, it returns right away without spinning out and the string will be wound tight. The tight wind really helps to get the next throw out with good power. I was contemplating switching off silicone bc the loose binds were starting to really bother me with ultra grey but I absolutely love the gear oil and will be sticking with that for my 1A yoyos.
Also one more observation to add while I’m comparing the two, but the gear oil also lasts longer than the ultra grey for me.