Thanks everyone for the many helpful answers and comments.
I'm always impressed at how easy it is to get useful information
here. I'm not sure how people survived before the Web and Usenet.

To answer the question that came up a couple of times, I'll be
flying a 1986 Socata Trinidad TB-21. Nice plane with reasonable ability
to get in and out of short fields, but can also theoretically cruise
at 187 knots at 25,000 feet. The theoretical part is that given
the O2 requirements for a mask, I won't really fly it that high.
Also it gets quite cold up there in a TB-21. For some of the
legs I'll fly with nasal oxygen at 16 or 17,000 feet and can
get better than 165 knots at that altitude (the POH says 175,
but I'm not convinced).

BWI had not occurred to me since I would not have guessed,
as several people have mentioned, that it is actually GA-friendly.
Despite that, I'm guessing it's a long haul from Bethesda, but
given Ron Natalie's comments about FME, I'm wondering whether
actual ground travel is faster there than I realized? If not,
based on the various comments, I'll probably go to GAI.

--
David Rind