Atm the reaper opencl code sucks. My 5870 generates about 420kh/s, to use as a reference. So it should be getting like 6-700 or more from a 7970.
But how many accepted shares does it generate at that alleged hashrate?
According to the pool, about 55k accepted since the night of July 18th ( almost 3 days now) but I also game on this box. I also have a tri 5970 rig that has 250k+ accepted shares. I've found that the thread concurrency switch in reaper has a lot to do with stales/invalids. Also the calculated pool speed is usually +/- 10% of 420, right now at 436.