I would try Philly in the late fall.  Pretty fast and a cool temps.  The great benefit here is that if you qual, you can run in two Bostons because you would qual after the year's close out.  So say you qual in Nov 2010 in Philly you can run Boston in 2011 and 2012.

I qual'ed in Philly in 2004 as a Clydesdale in the 35-40 group (3:12:07).

You might also consider the California International Marathon in Sacramento. It's in December, very cool, and a net downhill. I ran a 3:07:20 and was third Clydesdale finisher. Qualified for Boston by 13 minutes. Only problem, Boston was already sold out for this year.