Comfort means what it says, it's the level at which a normal person would sleep comfortably. Limit of comfort - which is the Apkit figure - is again pretty much what it sounds like, the coldest level an average sort of person can sleep comfortably. Extreme rating is just about staying alive in a cold and shivery marginal sort of way, but Alpkit doesn't quote that one,
It kind of depends on your to be honest. The Pipedream 400 is about right for me for three-season use, maybe with an extra top and hat if things get cold, but people sleep at different temperatures, some feel the cold more, if that makes any sense. I'd say yes, it should be fine unless you're someone who sleeps on the cold side.