Travel bag for 40D + 17-55 only?

Is the 5MDH the smallest bag you need for a 40D + lens and possibly a flash or can you go smaller still?

Depends on the lens. The Domke F5Xb will take my 20D and 24-70 along with the 580EX flash in the main compartment; it's an inch or two smaller than the Crumpler in width x height and about the same length.

I can fit my 10D + Tamron 17-50, Tokina 11-16mm (under the camera grip), and my 580EXII with case and extra things like extra batteries, filters and more in my 5MDH.

My cousin regularily fit his 40D + lens (17-55 or 10-22 most likely) and 430EX (folded to an L shape) in his 4MDH. It's a tiny bit of a tight fit, but small and compact.

gool wrote in post #9170714
I can fit my 10D + Tamron 17-50, Tokina 11-16mm (under the camera grip), and my 580EXII with case and extra things like extra batteries, filters and more in my 5MDH.

My cousin regularily fit his 40D + lens (17-55 or 10-22 most likely) and 430EX (folded to an L shape) in his 4MDH. It's a tiny bit of a tight fit, but small and compact.

Your cousin's setup sounds perfect for me. Thanks!