That's including the GPU ([Nvidia] EVGA GeForce GTX 680 FTW+ 4GB) running one task for MilkWay@home at a time as well as the CPU running 12 (one per thread) at a time.

Ahhh okay thanks. How many gpu tasks at once are you running? With an app_info file you might be able to run more than one at a time. I do NOT know how old this one is but here is an example of one for an Nvidia gpu for MW:
<app_info>
<app>
<name>milkyway</name>
</app>
<file_info>
<name>milkyway_separation_1.02_windows_x86_64__opencl_nvidia.exe</name>
<executable/>
</file_info>
<app_version>
<app_name>milkyway</app_name>
<version_num>102</version_num>
<flops>1.0e11</flops>
<avg_ncpus>0.05</avg_ncpus>
<max_ncpus>1</max_ncpus>
<plan_class>cuda</plan_class>
<coproc>
<type>NVIDIA</type>
<count>0.5</count>
</coproc>
<cmdline>
</cmdline>
<file_ref>
<file_name>milkyway_separation_1.02_windows_x86_64__opencl_nvidia.exe</file_name>
<main_program/>
</file_ref>
</app_version>
</app_info>

This line "<avg_ncpus>0.05</avg_ncpus>" lets you run two units at once, changing it to 1.0 changes it back to one unit at a time OR changing it to 0.25 would allow it to run 4 units at once, 0.33 would be three units etc. You would NEED to check out how much memory the card is using prior to making any changes though. Gpu-z can do this and it is free. IF it says you are only using, for example 400mb per work unit, then your 4GB card is being VASTLY under used! The newer versions of Boinc, currently in Beta from 7.0.40 and above, use a different tile to do the same thing but it does NOT force you to use the anonymous tag when running a unit. You can download all version of Boinc here:
http://boinc.berkeley.edu/dl/?C=M;O=D