I think it depends on the nature of the job and whether or not I "own" my work.

If I "own" my work in some capacity, e.g. a freelancer, a co-founder, getting public recognition for my work, getting to publish papers in my name, getting to talk about my work in public, get the chance to open-source my work, then I'm happy working more.

If I work for somebody else, or some big boss always takes the recognition for my work, as is often the case in some large companies, then I'd probably be much happier on the <40 side so I have time to learn and build things that are truly my own, outside of work.

I think 20-40 might be a sweet spot for certain fields where creativity drives money. In those cases, rest and recreation time are paramount to work productivity.

We only question hours/week > 40. It's edgy and cool. Past that, you are looked upon as a sluggard or kook.