I was planning on posing a similar question, although I'm way ahead of myself. I'm going to be running the Loch Ness Marathon on 29th September again this year.
About 5 weeks beforehand there's a local 17.5 mile coastal (very hilly) challenge that I competed in last year.
I was thinking about incorporating it into my marathon training, but not sure how to treat it. I thought the thinking would generally be "treat it as a long slow run", maybe with some MP sections.
But, maybe it would be okay to race it? I fear that I might get carried away on race day and just go for it. Would that be too close to the marathon?
Last year, my marathon plan didn't exist - I was blagging it big time. I raced the 17.5 mile coastal challenge (well - I say "raced" - I went all out and did it in as fast a time as my fitness level allowed!).
I realise I have a lot of time to think about this...