Putting the cart before the horse

Today was the day I was going to add in a speed workout. Repeat miles sounded good, as I knew I could keep the pace a bit slower than if I had went with repeat 800's. Off I go and realize very quickly that I have no idea what I want or need for a pace. If it were just the Hyannis Half I was training for things would be easier, but I have no idea what to expect for a half iron man which is the real goal of all this training. My PR for a half is just under 2 hours but that was several years ago and I didn't swim or bike beforehand. I'm also not sure that sprint races are a good gauge either, the distance doesn't really compare and I never took the training seriously. But lets be real for a moment, IF I register for the half iron man and IF I get to the start and IF I finish I likely won't give a damn about pace and will be overjoyed with a finishing time. So again where do I start with speed. 8 miles last weekend was at a 10:32 pace which would get me a 2:18 half. SO do I go with 10 min pace for repeat miles and a 9:30 for the 800's? I also figure that in a half iron man my running pace will be at least a min slower meaning that an 11:30 pace would bring me in at about 2:31. Now I've only confused myself more.

Miles run today: 4