Use reaper. The reason is that cgminer does not support large thread_concurrency values, which can be required for effective mining with 78xx and 79xx cards. cgminer can be useful for 77xx series cards or the 7970, the latter for which no optimal reaper configuration has been found yet.
CGMINER: Use a comma to separate thread-concurrency values, eg. --thread-concurrency 3200, 8000. Values correspond to the card number in zeroeth order.
Not sure if it will help you much.