I have the hacked firmware and the 420EX. I agree that if you can't set FEC it won't be a good match; when set to 0 I rarely get a really good exposure. For shorter ranges I leave it around -2/3 for most subjects and it works well there.

Here's a link that shows you some digital rebel flash shots with various FEC settings:
http://host.whereuhiding.com:9080/ca...l_FEC_Test.htm