So I just discovered there is an inaugural Hamptons Marathon this year, scheduled for Saturday, September 29th.
The course seems like it will be affected by the wind more than anything else, running mostly around the Amagansett/Montauk peninsula. The elevations changes are bunched here and there ,with a fair sized hill at the start and at miles 18 and 20.
Like everything else in the Hamptons, it ain't cheap- $85 through June 15th, and $95 after.