When to re-balance a motor?

The rings are lighter. I would let it go. It isn't worth it.

I balanced all my race stuff to under a gram but that's just because I have mental issues about stuff like that. I know other builders on race engines that when they were under 6 grams they stopped.

There is a lot going on with oil slinging around, crank deflection and other things that make for a bunch of mental masturbation.