Intervals and speed work are not exactly synonymous with ultra distance running, but I seem to have reached some sort of a stalemate. Looking at my training over the last few years, I really don't think I could squeeze in a whole lot more, juggling a full time (and busy) job, along with family commitments. From all that I have read, there are a couple of ways to get faster: lose weight, and throw in some speed work.
As far as the weight loss goes, sitting at around 155lbs, I think I'm where I want to be, though I have informally set a goal of 150lbs by the time the Leadville 100 rolls around in August. So I guess it comes down to doing some speed. I talked informally to a coach, and he is of the belief that 4-6 x 4-6minute intervals at 88-92% MHR is the way to go for an ultra, but I'm very open to other suggestions.
Guess I need to go figure out my MHR! Somehow!