I don't think time worked linearly correlates with profitability, especially when talking about long timeframes. E.g. working 120 hours per week for a year is extremely unlikely to result in 3x the productivity as 40 hours a week. Same with working 3/5ths as much, it's unlikely to linearly scale down to 3/5ths the value (not that "it can't ever", just not as a typical expectation).

That aside, plenty of places offer a 4x10, or are fine with it when asked, and I think that's a more productive way to put in 40 hours each week while also being more convenient for yourself (before even getting into wanting to lower total hours).