You've running an unbelievably high overclock compared to my 7970 getting 500k/hash with reaper.

925 mhz core is default, you're at 1275 mhz. that's a 38% overclock.

500 k/hash * 1.38 = 690 k/hash. I'm thinking that reaper might still be a bit faster, clock for clock.

I don't want to OC my new 7970's. Otherwise i'd test it myself.