Do those two megapixels really matter? I wanted to find out for myself so I shot the moon with a 300 F/2.8 AFS II + TC17E-II. Shot 20 minutes apart, both images at F/8. For both cameras, no in camera sharpening, normal tome comp, sunny WB. Shot in Raw, both images tweaked with an identical slight S curve applied by a user defined setting and USM 57/5/4 in NC. The D70 image was shot 1/3 stop slower so it's exposure was tweaked + 1/3 ev in NC. In all other ways the settings are as identical as possible.

The composite image is all 100% crops. It includes the original images, at 4 and 6 mpx respectively before cropping. It also includes a D2H image upsized to 3000x2000, and both images upsized to 4000x2629.

I see a very slight difference in sharpness, favoring the D70. I can easily tweak out that difference but I did not want to tweak individual images; that is your job if you care to download the images and play with them.