Well firstly, why only 4 nights not 7?
To be honest, although people can share their arrangements I think it all depends on the personalities of your children. And lots of children can adapt to several arrangements.
I actually think it's pretty important to think about what suits you, too. Long, like when you have a new partner. Personally I think every Sat means that neither of you ever get a totally free weekend. Fine if you are flexible with each other. But personally one of the only "up" sides to not having my child very day
is getting to go away for the weekend occasionally. So my advice is to think about you.
My friend's kids switch houses really frequently. It would drive me nuts as a parent and I expect as a child! But their decision is so that they never go more than 2 days apart. And it works for them.
My arrangement is more flexible because I work abroad. So she does Sun-Thu in week one, and Wed night only in week two and three, three week pattern. Occasional weekends with him - maybe 1 in 4 or 5? Frankly none, when he didn't have a girlfriend he wanted to play superdad to 
Some people would think my arrangement is a bit of to and fro, but my 6yo is happy. She very much sees herself as having two homes, not one that she lives in and one which she visits.