I have purchased severalsleeping bagsthrough Sierra trading posts, and have never been dissapointed. Of course, a down bag is going to be lightest and most compressable. But is useless if you get it wet. The bag I use for backpacking is a Sierra designs 0 rated polarguard 3D. I have been pleased with it. One of the most important things about buying a bag is getting a comfortable, breathable inner lining. If you don't, your sweat will stay in the bag and make you cold. Sierra designs have a comfortable lining for me. Polarguard is also pretty close to down as far a copressablity and weight, but will retain its loft even when wet. However, you can't leave it in a stuff sack for any length of time or it will lose its compressablity. All synthetic downs are that way to a certain extent, but they are getting better. However, an old sierra designs bag that had lost its loft was sent back to them and they sent me a new bag! I hang my bags upin the off season, and carry them in a loose bag when in transit. I only put them in a compression bag when I arrive at the trailhead and head out. Doing this, my latest 0 bag hasn't seem to lose much if any loft in about 8 years.

I have a Cabelas XPG tent that have served me well. However, it is a 3 season bag about 8 1/2 lbs. That is the rub though, to go up to a 4 season tent jumps you up to over 13 lbs. I don't know of any way to avoid the weight jump when going to a four season bag.