Interesting route. Preston Park is big enough to accommodate all the runners/ baggage trucks etc. It takes in The Pavilion (had to really, what else has Brighton got to show off?), but it also goes through some major shopping areas such as London Road and New Church Road, which I assume will need to be closed to traffic.
I think overall it's pretty good as a road marathon route. Only bit I'm not sure about is the blip through Ovingdean @ mile 8.
But as you say Sweder, it clashes with a possible jaunt to de Emerald Oisle.