>Thanks Linwood, I find that the 400 is not always long enough >for small birds and I have had to crop severely and the noise >and quality of the cropped image is pretty good. I know the dx >mode would give a larger image but would the noise level be >manageable?
I believe (and it is more belief than science as I have not tried as I sold my D300) that the noise level will be lower in the D800 for an equivalent number of pixels with all other things being equal. It's a 6 year (+/-) newer sensor, and about the same pixel density. My guess is you will see almost a stop less noise.
I notice the above image is at ISO 1400 but at 1/8000th of a second, so bringing down the ISO will get rid of the vast majority of that noise. Even a quickly moving sparrow probably doesn't need 1/8000th (that's assuming my exif viewer is right, it's giving me an add fstop so maybe it wasn't).