Fit is very good, but you have to accept these are performance tights with substantial compression, you're not going to able to just throw them on. Take your time, and wear them around the house a bit when you first get them and they'll loosen up and conform to your body. Size is dictated waist measurement, not how tall you are, how much you weigh, what size you take in Pearl Izumi, Louis Garneau, Assos etc, it doesn't matter. Just use the Castelli chart for a perfect fit.
The ProgettoX2 pad is great, so that's a good reason to get them by itself. However, these don't keep me warm down to Castelli's rated 32 degrees. They make riding at that temperature possible, but I feel the cold more than I like. Their comfortable temperature range seems like high 30s to mid 50s, at the most. If you're OK with the Kiss3 pad get the Ergos, or any other Castelli tight with Thermoflex, temperature range is the same, although these do have a bit more compression and "vanish" more than the Ergos. I like the ProgettoX2 better so these are worth it to me for rides over 2 1/2 hours, shorter than that and the Ergo/Kiss3 works almost as well.
Update 2/2016: after using these now for 1.5 winter seasons I can say these are definitely not warm enough for mid/hi 30s and down. And they barely work from 36/37 to low 40s. Their main problem is they let wind right through, no wind blocking at all. Best temps are really about 42/43 to mid 50s. Still nice tights when used within their capabilities. The Ergos I mentioned above are a bit warmer and block wind better, but with the caveats as noted.
Update 12/2016: 1) These are wearing very well. No loose threads, seam separation, holes, decal delamination, etc. Still basically like new into their 3rd year of use. 2) It's probably me, but I'm going to adjust my estimate of their lower comfort limit up to mid 40s, and even higher if it's very windy and no sun. They are just not true winter tights, rather early spring and late fall. Their two virtues continue to be the excellent pad and low constriction for a full tight.