Thanks Bill. What I'm hoping to achieve is lower noise for D700 equivilent ISO's on an APS-C sensor and I know that's no easy task with the small sensor. As I've mentioned, I am hoping the D300s replacement will offer this. My concern is that when it does arrive it will be the 16Mb sensor that's in the D7000. Hopefully, it'll have an updated processor etc. Fingers crossed, but it can't come soon enough for me.
Failing that I shall probably keep the D700 in FX mode with its reach limitations and just accept that I'm am only going to get the images I want by getting closer. That's never easy with birds in flight!