Keep in mind that the sharpening in camera will only be used for jpgs and in Capture NX2. Other raw converters generally ignore everything in camera settings except for white balance.
Many people set their camera sharpening higher than the default. I personally set mine to 5.
The reason why the D800 seems softer is that you're capturing a lot more fine detail and that details will seem a bit softer. As a simple exercise, resize the D800 file to the same dimensions as the D700 and then compare the images. They'll be very similar. And you'll be comparing apples to apples.
Also the D800 is more demanding on your technique than the D700. It can make your errors, especially slight camera motion, more obvious than in the D700. It just takes some getting used to.