I know it's a rather privileged thing to say, but I just passed up a job opportunity because I don't want to get back to 30 paid vacation days. Once you get used to 47 (took a voluntary paycut of 5 percent for 12 extra days), where you get so many side projects done because you have the time, it's hard to go back to the normal 28-35. So I have no idea why the US rarely goes above 20 or whatever they have.

I dropped to a four-day week (with 20% pay drop so in the same ballpark as your 5% for 12 days off) for stress reasons “temporarily” almost exactly two years ago. The burnout problem is finally looking like it might permanently recede (family health matters are much more stable, some work matters have been addressed, I've sorted a few personal things out, some external problems have been fixed or just told to fuck off, etc.) but I think I'm going to stick with the four days week as long as I can.

The extra money would be very useful to me right now, but I'm surviving without it and the three-day weekend is really working for me. I'm even finding time to relearn a second language on case the UK follows the US too far down the full-fash route and I feel the need to get out of dodge [I refuse to be the sort of Brit who rocks up everywhere expecting everyone to speak English!].