I'm 5'7" and weigh 150 lbs and the small fits well.
These tights are spendy indeed, but I have a real tough time with my legs getting tight in the damp cool air of the PNW regardless of activity when the temps dip below the mid 40's and CW-X really seems to help. Much more than "regular" running tights I've used in the past.
I have been using these as running tights so far and had hoped to use them in place of silk weight capilene for skiing this winter. They may not be warm enough for that. If it is below 50 degrees out and especially if it is windy, I wear my Sporthill 3SP pants over the tights and have had no overheating issues at all. Based on my experiences so far, I would not hesitate to get a pair of insulator tights for the cooler weather.
They really seem to shine in the recovery period after I run. I feel great. Tired but fresh all at the same time.
I haven't had any chaffing issues with mine.
If you feel like dropping the cash, I think they're a good investment. Recommended.