Looking into purchasing two 7970's for a LTC mining rig myself. Any suggestions on brands? Are you guys running them "underwater" or simply keeping them air cooled? If so, does it help with the hash rate? Is it worth the additional expense for the blocks? Does this help with energy efficiency?
The cost of a water block alone can be 30-50% that of the card. So it's more effective to buy another card.
As far as temperature vs. consumption goes, you can save up to 30W on a card by going with temperature down from 80°C to 50°C.
As for the 7970 cards, it needs to be a new model with a new BIOS, that is the most important thing, because basically the silicon has been updated twice, the last time in April 2013, and the BIOS too. A simple thing: check the BIOS version, the new cards do not have any alternative BIOSes, and run much cooler.
Use the lowest possible voltage on a card, on reference cards such as Sapphire, the second BIOS - when the button is pushed to ON position is the good one, that allows you to do things right. Basically the card you want ends in OC or something like that. Don't buy stale cards made in early 2012 for example
