I have a Kelty Lightyear Down 20º bag. It's about the same but had a slightly higher grade down (650) than the Cosmic when I got it a couple years ago. It's a very nice bag for the money, and I'd expect the Cosmic Down bag is every bit as nice.

I'll add that I'm not much bigger than you and I think the bag is a bit tight in the shoulders. I'm around 5'9" and 140, and it's not at all too long, so it'd probably be perfect for you. I don't think you'd find it too big in any case.

Mine is warm and cozy down to 32º, and chilly at 20º but not really what I'd call cold. I've layered up with warm bed clothes in it at 20º and was plenty warm, but a little tight in the bag.

I really can't compare it personally with other bags in the same price/weight/cost range because I've not used any, but I did do a lot of reading up on them before I bought mine and I'm very happy with it.