I currently use 2 SB800 for residential real estate shooting in Brooklyn, NY. My other go-to equipment includes the D300 body and 14-24 f/2.8 lens.
I'm not sure if I should or need to upgrade one of the SB800's to an SB900. Based on my equipment and shooting interiors/architecture being my main use for flash, can you see any tangible benefit with an SB900? I am trying to think how my customers would benefit from such an upgrade. I don't see myself upgrading to a D700 any time soon.
For my personal work I use flash maybe 5% of the time. I don't mind making the investment, but I need to justify it and know that it will pay for itself through improvement in the light quality or my work process. Thanks for any feedback!
I would say you probably don't need one unless the following applies to you:
1. You need more power, which the SB900 will provide in essence, for your DX sensor. Of course you could achieve the same with an SB800, if you manually zoomed to match the lens, but that would be a pain.
2. You need a third flash for lighting large interiors.
It remains to be seen whether the even lighting setting will give better illumination from edge to edge, albeit at a loss of power.
Scott Chapin Powder Springs, GA, USA Nikonians Team Member
One feature of the SB900 that got my attention is that it has overheat protection when doing rapid-fire shooting. Since that is my style often, this in itself is enough reason to go from an 800 to a 900.
From what it sounds like you're doing, this is probably not an issue.