Jed there has to be something else wrong. The 58XX will always be issued the HUGE wu that pay 6k. Even if it was issuing smaller wu your credits wouldn't drop that much because you would complete them much faster.

What you want to check is the GPU loading on your card. If you reserve a thread for the GPU the loading should stay between 95-98%. If you are running 100% CPU crunching and Moo then you will take a major hit on the GPU output. A 5870 running at 950 MHz will produce somewhere around 380k per day on Moo. At 850 MHz it does something like 350k ... I can't give you the exact figures anymore because I'm also running the cudas on Moo.

What I do is use the program "ProLasso" to reserve a thread for Moo (affinity 7 on an I7) and set the priority to HIGH. Then for the Nvidia I set it to run on threads 0-6 also at HIGH priority. On the CPU tasks I drop the "use CPU %" to 90 which then only schedule 7 CPU tasks. Using ProLasso I set the priority to "Above Normal" and the affinity to 0-6. Doing this clears a thread that is only used by Moo.

On the machines with 5970s I have to reserve 2 threads (1 full core) to Moo. Running the 5970 or 2 5870s Moo will use 25% of the processor by itself. If you don't reserve this then you will take a major hit on GPU output.