I have been fortunate enough to work a 4x10 shift for my employer for the past 6 or 7 years. At this point, the shift and hours are almost worth more to me than the actual job I am doing since having the three days off makes for a much more relaxed weekend. Being off for one or two weekdays when most everyone else is at work is also a definite plus since it makes getting errands done and just going out and being a "tourist" in my own city much easier.
It's exactly what I'm thinking about lately. A lot of colleagues of mine work 4 days a week, from Mon - Thu, and have 3 days off. It is a HUGE difference compared to the 5:2 ratio.
It's not that I don't enjoy my job, but it sound so much sane to me. I hope next year I'll have saved a little bit of money I currently need so I'll be able to do a 4 day working week.
If you ever have the opportunity to work 4 days a week, choose Tuesday to Friday, rather than Monday to Thursday. The reason is that everyone else will be in a good mood on Friday so it will be much less stressful working Fridays rather than Mondays. For the same reason, don't burn your floating holiday on a Friday.