I tried both the Hydrogen and Helium, and found the limit on both to be 5 or 10 degrees higher than the advertised rating. I didn't have any problem with excess length, though. I found the half-zips to be particularly annoying.

After I got my first WM bag (a Mitylite, for summer), I quickly decided to get a Megalite, and I've never been tempted by any other bag since. (Well, there was a one-night-stand with an MSR Ventra, but my Mitylite knows all about it and has forgiven me; there will be no future transgressions.)

My wife, who rarely camps, liked the Mitylite well enough that she made me get her one for when the power goes out in the winter. Since then, she's started using it when all the kids and grandkids come home at Thanksgiving, and we end up sleeping on the sleeper-sofa - she doesn't have to make it up with sheets and blankets. Now, that's an endorsement for WM!