When I read the previous comments from earlier years that seemed to be the general consensus - that yes, it's flat, but because of potential congestion etc. it was quite a bit slower than a true road half marathon.
I've got no more evidence than that but have in my head that if I can drag myself through in around 2 and a half hours I won't embarrass myself too much! Looking at results from previous years there seems to be a really good spread of runners and loads of slower runners like me.
Worryingy I'm on holiday for the 2 weeks prior to the race and only come back on the Wednesday so at least I'll be well rested and well carbed up (too much Greek beer and pasta), but if I can get my long runs done before I go I should be OK