In my previous post I compared the Nikon D700 and D300 cameras using the concept of equivalent images. In that test I used a single lens, the Nikkor 70-200mm VR, to compare images from the two cameras. I used the same lens because that was my only way to obtain near perfectly matching Fields of View (FoV) - the D300 and D700 are slightly different size, and placing them on a tripod does not give the same perspective. However, with the 70-200 I was able to mount the lens to the tripod and therefore get much closer FoVs. The problem with my comparison images in the previous post is that the Nikkor 70-200 is much better suited for DX than for FX.
In a more realistic scenario, you would use equivalent (not the same) lenses on each camera to really see the differences. Here, I attach a Tamron 28-300mm f/3.5-6.3 VC to the D700, and the very popular Nikkor 18-200mm f/3.5-5.6 VR to the D300. The lenses are not exactly equivalent, since the D300 would require an 18-200mm f/2.3-4.1 for equivalency, but are representative of actual choices available.
In these comparisons, I did not use a tripod. I did not force equivalency to extreme levels either. Rather, tried to capture the same image by setting the cameras using aperture priority (1 and 1/3 stop down for the Tamron), and getting as close as I could to equivalent focal lengths. I set both setups with auto-ISO's that attempt to maintain at least 1/30 sec. I set the maximum ISO on the D700 to 6400, and on the D300 to 3200. Thus, in at least one of the comparisons, there is significant shutter speed difference. I think this kind of comparison captures much better what could be expected in actual use.
D300, Nikkor 18-200 VR, 2000mm, f/5.6, 1/30 sec, ISO 1251
D700, Tamron 28-300 VC, 300mm, f/9.0, 1/30 sec, ISO 3200
In the pair of images above the D700+Tamron are a clear step up to the D300+Nikkor. Less vignetting, sharper. Just looks better.
D300, Nikkor 18-200 VR, 48mm, f/4.5, 1/30 sec, ISO 1600
D700, Tamron 28-300 VC, 78mm, f/7.1, 1/30 sec, ISO 4500
In the two images above, the D700+Tamron improve on the D300+Nikkor even further. Less noise, better colors, sharper, and no flaring.
D300, Nikkor 18-200 VR, 135mm, f/7.1, 1/30 sec, ISO 2500
D700, Tamron 28-300 VC, 210mm, f/9.0, 1/25 sec, ISO 3200
I goofed in trying to set up equivalent images in the comparison above, but this is bound to happen in regular use as well. The D700+Tamron should have been stopped down to f/11, not to f/9. So the depth of field should have been larger and a larger ISO should have been required. Nonetheless, the D700+Tamron are a definite step above in sharpness, color, and noise.
D300, Nikkor 18-200 VR, 150mm, f/10.0, 1/13 sec, ISO 3200
D700, Tamron 28-300 VC, 220mm, f/16.0, 1/6 sec, ISO 6400
This is another case where the D700+Tamron clearly outdo the D300+Nikkor in every possible aspect. This is despite a full stop difference in shutter speed, an indication of the significant effectiveness of Tamron's VC (Vibration Control).
D300, Nikkor 18-200 VR, 50mm, f/4.8, 1/30 sec, ISO 720
D700, Tamron 28-300 VC, 78mm, f/7.1, 1/30 sec, ISO 1600
In the two images above, the D700+Tamron show off yet another area where they improve the D300+Nikkor: Constrast in addition to lower noise and sharper images.
I hope this practical comparison has shed some light on the currently available super flexible walk-around options. I use mostly Nikon glass, but the Tamron 28-300mm VC attached to the D700 clearly outperforms the Nikkor 18-200mm attached to the D300. The Tamron has yet another characteristic that was not explored here - it is a macro lens too (it can do 1:3 magnification at 300mm)!