Onetit, I know exactly what you mean about looking at your feet and fearing a broken ankle...I'm getting over that, a bit...now that I have excluded any concept of ' a time' from my thinking. That doesn't augur well for trail races but it's making the actual running more and more enjoyable.
Iain, tartan' did the Marine Corps this year...getting stranded by the hurricane into the bargain...and raved about it.If you change your mind, her race report might be handy. I think it's the only other mara' that I'd really, really like to do.
James, you seem to have identified quite a few of the probable causes of your disappointing run.You'll do it differently, and better, next time. And you did run 17 miles! Well done...I know i'm not the only person to have noticed that the 17-18 milers are 'different' from everything that's gone before. I bet the next one...although longer and, therefore, more demanding...will, bizarrely, be 'easier'. Just you wait and see 
Right, E. 'Off to read your Report..