I owned the Madden Girl Zoiiee boot in brown with the red zipper and have worn them until they pretty much fallen apart, I decided it was time to upgrade to the real deal and the black with a red zipper is my dream boot.  I have large calves, and the Zoiiee boot was perfect, I had a real fear about ordering these online because it has happened more than once that I can't zip up a knee high boot.  I ordered the Z boot in a 7 because they ran big, I ordered this one in a 7.5 and it fits PERFECT! From the moment I put them on, they have been so comfy!  They fit snug around my foot in a supportive, not painful way.  They hit right at my knee (I'm 5'7") and they zip up fine over jeans. Right out of the box it was a little snug, but after 10 hours of wear, the next morning they went on just fine without any zipper struggles.
The only reason I would not recommend these boots is because they are so cool, unusual, and garner SO many compliments (I can't tell you how many times I've been stopped to be told how awesome my boots are) I want to be the only one wearing them!