My longest run was also 20 miles. I finished in 5.20. Just before the start a seasoned runner asked me how far I'd gone and told him my longest run was 20 miles and he said to me that was plenty. I guess everyone has their own opinion. The fact of the matter is, if you want it enough and you've done enough training for your mental ability to push yourself to complete it, then you will complete it. Well done to your wife, Gareth.
2006 was my second GNR. Last year I struggled and did a run / walk thing, so I have a great deal of sympathy for those who feel the need to walk at points. What does annoy me though is when you have three or four walkers in a line across the road all chatting and blocking up the route. To me this is disrespectful to those who do want to run. We all run for different reasons and we all have different levels of ability and the GNR really highlights this. It would be great if all participants could remember this and respect those at the other end of the ability spectrum from themselves. And for the record I'm a plodder but I accept this and ensured that I was in the correct pen (orange) for the time I'd listed myself at. Yet at three miles in I was overtaking people who had been in the pen in front of me (green). Quite clearly the person had not been honest either with themself or with their entry form.