Usual preface, I’m with PreciseBits so while I try to only post general information take everything I say with the understanding that I have a bias.
This gets confusing as not everyone uses the same standards. Some manufacturers/sellers will just use “balanced for “X” RPM” and some will use ISO 1940-1 “balanced to G"X” at/for “X” RPM". The first one you are taking the manufacturers word for it being good to that RPM. For the second version is listed the residual unbalance at that RPM. This makes the ISO version an empirical measurement that can be applied to other RPMs. e.g. G2.5 at 20KRPM is ~G6.3 at 70KRPM. There’s some more discussion on this here if you’re interested: Source for good quality ER11 collets . Starts about collets but gets into nuts further in.
The above makes it hard to compare some nut balances and without a lot more info it’s hard to know what you “need”. The short version is the lower the “G” value at the same RPM, or the higher the RPM at the same “G” value, the better balanced the nut. If it just says "balanced for “X” RPM, you are just taking the manufacturers word for it. So weight that as you will.
Also, thanks for the shout out Griff, I appreciate it.
Hope that’s useful. Let me know if there’s something I can help with.