I am doing 3-day work week (plus a day of studying) per week, so roughly equal, and it has worked great. You're more focused at work, and you get a lot of time to think about problems before having to sit down and do it.

Right now I'm working Wednesday through Friday, but if I had a choice of four days I would have Wednesdays off. The extra day in the middle to take some time off and thing about other things and get back with a new perspective worked very well for me when I had the opportunity, better than the concentrated block.

Right now I'm doing three days in a row because my boss thinks it's easier to communicate that way, and I guess he is right too, it's a trade-off.