Marathon of the sands

I have been talking wildly about doing this thing.

It's probably a bit stupid, or it may just be talk, but I have until 5th March to make up my mind because that's when you have to pay a very large desposit.

So anyway, to do that I would have to do lots of marathons. I'm doing London this year, but I really, really want to go to the US this year and do one there. But where?

I want to run a fast (for me) time of around 3:15 so preferably a flat course, not too hot (yes I realise the Sahara is likely to be hot…), and want to see a new, fantastic city and to stay for a few days (at least) afterwards for my American fix and to eat some jujy fruits.

Any ideas?