Lots more megapixels (photo)
8.02% more megapixels (photo)
Notably larger sensor
24 x 36 mm
14.9 x 22.3 mm
2.60x larger sensor. The larger the sensor the more light the sensor captures yielding in better image quality.
Considerably more focus points
2 more focus points. The more focus points the more flexibility in picking which part of the scene to focus on. They also give the image sensor a better probability in identifying the right area of the scene to focus on in more automatic modes.
Distinctly lower noise at high ISO
2.95x lower noise at high ISO. The maximum ISO at which the device still captures excellent quality images. Source: DxOMark.
Considerably faster shooting at highest resolution with AF as JPEG format
21.62% faster shooting at highest resolution with AF as JPEG format. Fast continuous shooting is useful for catching action shots.
Measurably better image quality
17 better image quality. A device's overall image quality score considers: color depth, dynamic range and low light performance. Source: DxOMark.
Explicitly higher maximum light sensitivity
8x higher maximum light sensitivity. With a higher light sensitivity (ISO level), the sensor absorbs more light. This can be used to capture moving objects using a fast shutter speed, or to take images in low light without using a flash.
Way better color depth
7.69% better color depth. The better a device's color depth the more color nuances it can distinguish. Source: DxOMark.
Has a stereo microphone
A stereo microphone allows to record audio files or movies in stereo without an external microphone.
The device can connect to WiFi.
Significantly longer battery life
650 shots longer battery life. CIPA is an independent, standard measurement that determines how many shots a camera can take before the battery dies.
Significantly more battery power
1.61x more battery power
Wider dynamic range
5.22% wider dynamic range. The better the dynamic range the system captures a wider number of values from dark to light leading to more details in low and highlights. Source: DxOMark.
Has a built-in HDR mode
It can automatically shoot pictures with a higher dynamic range (HDR).
8.50 mm thinner
GPS enables global positioning, useful in map, geo-tagging or navigation apps.
Device is protected with extra seals to prevent failures due to any kind of weather.
Marginally more viewfinder coverage
2 % more viewfinder coverage. With 100% coverage you can compose the image correctly when you capture the photo. With less than full coverage you may have to crop your photos afterwards to get them looking perfect.
Newer DIGIC version
Newer DIGIC version. Newer image processors are better at processing multiple tasks simultaneously, and can produce higher quality images with better low-light performance and faster AF.
You have got the wrong specs for the 1Ds Mk III
You have compared the 6D with the specs of the 1D Mk III not the 1Ds Mk III which is a 21 MP Full Frame