+1 on intervals.
Short, sweet, to the point. You don't need the long rides, you need the ones that give you strength. Intervals are your friend.
When I do a 45 min. hard interval I think I didn't do enough, yet it's just enough, and I either recover or take the next day off. Intervals are demanding and sometimes we don't respect them as much as we should.
And big john, nice pic! I have to drive quite a ways to see that much snow.