For Landscape and Macro work there is very little difference between these two. That is assuming you are shooting RAW and manually focusing as is often the case for those two types of photography. The resolution difference is only about 2.4% in favor of the older 5D Mark II.

At ISO 1600 and below the differences in sensor image quality are minimal. Above ISO 1600 the 6D has a little better dynamic range than the 5D II. But as is the case with pretty much every digital camera when dynamic range at high ISO is compared to the dynamic range at lower ISO settings of course neither camera has near the same dynamic range at high ISO. A direct comparison of sensor performance can be seen at DxO Mark. As always, click 'Measurements' and then the various tabs for 'sensitivity', 'SNR 18%', 'dynamic range', etc. to see the measured data.

Improvements made to Canon's (or other parties) RAW conversion engine since the release of the 5DII can be applied to RAW images from either camera. If for some reason you desire to save your files converted in camera as JPEGs the 6D presumably has a little better JPEG performance. The same is true of the auto focus performance of both cameras. The 6D has a little better AF performance than tbe 5DII but neither camera approaches the advanced focus system of the 1D X or the 5D III or even the 7D. Functionally the AF systems are very similar in terms of number of AF points and the way they can be set up by the shooter.

The 5DII has both a higher maximum shutter speed (1/8000 vs. 1/4000) and flash sync speed (1/200 vs. 1/180). This points to a faster curtain transit time for the shutter in the 5DII. This could affect the way images of fast moving objects appear since the total time needed to take the shot is the time it takes the narrow slit between the curtains to transit the sensor, not the time any particular spot on the sensor is exposed as the slit between curtains moves across the sensor. The 5DII also has a higher shutter durability rating (150K vs. 100K shutter actuations).

The main differences between the 6D and the 5D II are in areas that do not directly affect image quality: WiFi and GPS capability for the 6D, SD card vs. CF card (some folks prefer one or the other), lighter/smaller vs. larger/heavier (some folks prefer one or the other). The LCD screens are the same size but the 6D LCD has about 13% more pixels (just remember all back of camera LCD screens lie like politicians anyway). The 6D is more flexible in terms of Auto Exposure Bracketing with up to 7 frames at +/-5EV while the 5DII is limited to 3 frames at +/-2EV. The range of exposure compensation for the 6D is 5EV vs. 3EV for the 5DII. Of course any of the exposure values available using AEB or EC with the 6D (plus those that use Tv greater than 1/4000) are available in the 5DII using Manual exposure mode.