GPU: HD6990 underclocked from 830/1250 to 738/1250
CPU: WindMaster's 4 year old dual Xeon E5450
Amazon says that's a $1000 card vs a $400 CPU, and Google says it's ~400 Watts vs 80 Watts (just a quick search, these numbers may be off), if anyone wants to calculate corrected ratios.
Good point! I'll fix my numbers.
^^ Have you tried playing with the lookup gap more? You should still hit faster GPU performance as by 8192 you will have moved off the CPU cache and are writing to RAM (maybe also L3).
I've played with it quite a bit. Also, nothing helped with 8192, it's all invalids.