So what is the general consensus on what temperature rating to shoot for when considering a three season bag? I'm a relatively warm sleeper and I'm looking (ideally) for a bag that will be comfortable from March/April through October in the Western US and Canada (Rockies, Cascades, Sierra Nevadas etc.) I have a thin synthetic bag for super warm temps (summer camping not in the mountains) but would like to be able to get just one other bag for everything else but cold winter camping. Is a 20 degree bag going to be too warm in summer temps? How far would I be able to push a 30 degree bag? What are people's opinons around here?
As a side note, the bags I'm currently considering are the WM Ultralite/Summerlite, FF Swallow/Hummingbird/Merlin/Osprey and the Montbell UL Spiral Down #1/#3. Any thoughts on these bags?

