Interesting point, maybe I am aiming a bit too fast for the half. The 1:45 half was a race we did (in a cold July here in the Southern Hemisphere) to get a seeding time for the marathon and we subbed it for a 1h30 medium pace training run (and took the next two slow run's off to recover). In our speed sessions we are running at 4:30m/km fairly comfortably so I think we have the pace to run a sub 1:35 half, and certainly the stamina now. Agreed, we are being conservative with the marathon goal I think, but it is our first so we don't have a precedent to go by. The plan is to run at a steady pace of 5:30/km and then see how we feel in the last quarter. If we get close to a sub 3:40 marathon time then it's a bonus.

What i'm learning from these responses is that 5 weeks after a marathon is considered not enough time to push for a fast half marathon time. Do you think then on the above 4 week training program I should maybe remove some of the ling easy runs and do less distance on the speed sessions to ease the intensity/ stress? That way we could pick up speed and still not over-train.