The most recent figures I've heard were that something like 40-60% of traffic (by bytes) on a dual-stacked client ISP will go over v6. I heard that stat about 4

The most recent figures I've heard were that something like 40-60% of traffic (by bytes) on a dual-stacked client ISP will go over v6. I heard that stat about 4-5 years ago, so it seems reasonable to expect it to be even higher nowadays. Another advantage is that v6 is easy to hand off early, but if you're CGNATing v4 then your v4 traffic has to go via your CGNAT routers. For cost reasons you probably want as few of those as possible, which means v4 traffic may need to go further to reach them. T-Mobile in the US is like this; v6 traffic is passed off as soon as possible and gets a relatively direct network path, but v4 traffic has to go all the way to one of their datacenters to get NATed. That can add a lot of latency.