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In Photoshop, go to "Image Size", and uncheck "Resample Image". Change the resolution in pixels per inch to 300. The Width and Height pixel numbers should be unchanged.

Note that the dpi figure is purely a guide to the printer driver software as to what size the image should be printed. It is more relevant to scanned images than to photos from cameras, as it allows the printer to give a print of the same size as the scan. When printing from a camera, you don't want a print the size of the sensor (about an inch wide), so the dpi figure can be set to anything you want.

The width and height figures will be greater for the D800E.

A Bayer camera has pixels which are not independent of each other. Instead of each red pixel being an independent measurement, it is a calculated value derived from neighboring pixels. In a Foveon sensor, each pixel gives three independent readings of the local light.

So the Foveon generates much more data than a Bayer with the same width and height. Maybe not three times as much, but nearly so.

The improvement is counteracted by higher noise levels, so at higher ISO settings the data are less reliable.