> GN of 12 meters for the built-in versus 21 meters for the SB-400, so the SB-400 can fire at 175% the power of the built-in.
Sounds impressive, doesn't it? 175% of the power or 75% more means that it is about two thirds of a stop better. That is, if you were at f/5.6 before, now you can shoot at f/4.2 now. I'll take it, but that's not really much more powerful.
> auto ISO programmed
I would caution inexperienced users not to attempt to combine auto ISO with TTL flash. Although it does work as it's designed, the interaction between the ambient exposure, the flash exposure and the auto ISO is complex enough that it's virtually guaranteed not to be what an inexperienced flash user would expect.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!