If you are looking to pay more than £1000 for your camera you are shopping at the professional end of the market. Cameras in this price bracket offer you ultimate control over your photos with a full range of creativity controls.
Improvements over cheaper cameras include better build quality, faster operation and better focusing control. You are also likely to find improved performance in lowlight situations. Another area where you can find better options is when it comes to shooting movies.
If this is your total budget and you do not already have some good quality lens it may be worthwhile considering dividing your budget between a cheaper camera body and a good quality lens or two. This is because the quality of the lens plays a major part in the quality of the photos you take and you are unlikely to get the most out of an expensive camera body if you couple it with cheap lens options.
The Powershot G1 X has a number of advanced features. These include manual exposure settings (Fully Manual, Aperture Priority, Shutter Priority), custom modes, RAW, a 4.5 frames per second burst mode and image stabilisation for both still shots and movies. High Definition movies with stereo sound can be recorded. The LCD screen is 3 inches in size and can be pulled away from the body and twisted round to find a more comfortable shooting angle. There is also an optical viewfinder.
The Canon EOS 5D Mark III is one of the most advanced Digital SLRs. It offers 61 point Auto Focus, the ability to shoot at up to 6 frames per second and has a 3.2 inch LCD screen. Shooting movies is taken care of by a Full High Definition movie mode, stereo sound and the ability to use manual exposure while recording. There is a socket for an external microphone and one for headphones. Canon have equipped the camera with weather sealing. The body is built around a magnesium chassis.