These knickers are excellent quality, but the fit is a little hard to nail down. I am around 6" and 170 lbs, and in Pearl shorts I am easily a medium. However, with these knickers, you have to consider the way the pant legs creep up if they are too small. All of a sudden, you are riding along with bunched fabric behind your legs! I tried the mediums out first and immediately had this problem. With the large, there is no problem at all!
I really like these bib 3/4 length knickers. I have older Pearl Izumi select knickers, these are more comfortable, the chamois is good and dense enough for long rides without feeling like a diaper. I am 5'9" 170 lbs and they fit perfectly.
These are definitely lightweight, perfect for my 45 - 60 degree riding here in the San Francisco Bay area. Straps are great! They do bunch up behind the knee when new, but get better with wear. Don't buy for really cold weather. More like a windbreaker on lower legs.