well 37.5 hours to 30 hours is 5 days a week to 4 days a week. You work 20% less but get 50% more off days, sounds like a great deal.

4 to 3 days, your productivity would go down 25%, and your vacation up 33% (3 to 4 days), so it's still interesting I guess but seems more balanced.

3 to 2 days, your productivity would go down 33%, but you only get 25% more off days (4 to 5 days).

My incredibly scientific analysis says that it would make sense down to 3 days a week, or 22.5 hours, but not so much after that.