I'm looking at this one as well for a potential first marathon and I'm local so would be very convenient. Should have done the half this year but couldn't in the end (just as well as it was such a grotty day they curtailed the full marathon and only allowed people to run the one lap for the half).
Eager to see if it's suitable for a slow first time marathoner!
I read on another forum that someone had measured the Coombe Abbey race and it came up as 8.7k. That would explain why I apparently knocked a full 9 minutes off my previous 10k time (was only my second 10k). Still, I really enjoyed it despite (or perversely perhaps even because of) the thunderstorm!