AMD has been making an effort at efficiency in its designs, but at the high end, many people don't care about efficiency all that much. So, reference is two 8-pin power connectors, custom high-end will have three of those power connectors. If they put the power connectors on the top of the card, then length of the card is less of a problem than it is when the power connectors increase the effective length of the video card. There are a number of features in the Radeon Settings as well that will allow for adjustments to power draw and speeds.
I have the feeling that these Sapphire cards won't be using the brute force approach of just throwing larger cooling systems at the card, and due to a lot of the expense of these custom cards is the physical size and weight, vapor chamber might help in a number of ways. We will know next week.