Robin Sibson , Sep 22, 2010; 06:35 a.m.
I use a 550EX quite happily with my 5DII. The only limitation on a FF body is that most detailed flash controls have to be set on the flash itself, and cannot be set from the body. I assume the same will apply to any of the early EX flashes. E-TTL II is a body capability not a flash capability, so if you camera body supports E-TTL II (and the 5DII does, of course) then that's what you wil get with any EX flash.
On a 1.6-factor body the situation is a bit different because flashes of the 550EX vintage (not sure about the 430EX) don't understand about smaller sensor sizes and on auto zoom will set the head to what any particular focal length requires for FF. That's always "safe" but does not make full use of the available light.