Seems dropping it and modifying other settings is dropping the temps and keeping the kH/s near constant.
You don't need high mem clock for mining, I run all my 7970's at 1125-1140 core with 1000 clock fan auto and I never hit above 80C and hashing at 670-700MH per card
He's mining LTC. Yes, you need a high mem clock for LTC mining.