I have a 20D and 5D (and soon a 40D!!) and 550EX flash unit. I want to add a second flash (430EX or 580EX) and just want to confirm that full wireless control will be achievable between the two generations of flash. I bought the 500EX new in 1999 and it is still going strong trillions of flashes later (OK, maybe a slight exaggeration).
Thanks for your help ,