Here’s an abridged version of 10-20 million and 30-40 million rows, and how many modifications they took before a stats update occurred. If you follow the PercentMod column down, the returns diminish a bit the higher up you get. I’m not saying that I’d prefer to wait for 20% + 500 rows to modify, by any stretch. My only point here is that there’s not a set percentage to point to.
And, because you’re probably wondering, turning on Trace Flag 2371 in 2016 doesn’t make any difference.
This is a good change, though as Erik points out, if you’re managing very large tables, you might already have the trace flag on and thereby won’t see any difference.