Agree. I went to a buddies house that had garbage balls. Nothing was right. He didn't know better, but I knew something was up. I took his set to my house to polish them for him, and weighed the balls. The CB was 10 grams heavier. It must have been a barbox CB, IDK. Anyway, those 10 grams made a world of difference.
The same day, I remembered that my Rempe ball was about 6 grams lighter than the Super Aramith Pro set it came with. So I played around with it for an hour or so, and again, the 6 grams lighter was very, very, noticeable.
In conclusion, I agree with most others, in that as long as the CB and OB's are within about 2-3 grams of each other, then all is good. But any further apart, and I think a high C to low B player can notice the difference in position play. That said, I wonder if a pro could notice the difference if they were only 2 grams apart. I was personally shocked how much of a difference 6 grams made.
And I was also mad at Saluc for making the Rempe ball 6-7 grams lighter. Its whole purpose is to practice stop shots and such. The mismatch makes it impossible.