7xxx series cards
Use reaper or cgminer versions 2.11.3 and up (see update below).  Set thread_concurrency to somewhere slightly below 64 * bus_width_of_card_in_bits.  So, for a 7950, that would be 64 * 384 = 24576; ideal values are 21712 or 24000.  Find your bus width here: http://en.wikipedia.org/wiki/Southern_Islands_(GPU_family)

To find the optimum thread_concurrency for your card, you will need to search above and below this estimate ideal value and see what is fastest.