I made a women's hat with very bulky yarn and used about 60 yards. I only needed 2 skeins to get the color changes. A man's hat would probably go well into the second skein. I hope that helps you judge how much yarn you need.
I've also used Atacama Alpaca. I think its really soft. I haven't tried Decadence, so I can't compare the two. I have a picture of mittens I made with Atacama Alpaca on my blog.