You pretty much have it, for the 4870 I simply have the avg_ncpu to 0.67, max_ncpu to 3, and count to 0.33. Using such gives 100% utilization. 6850 though I can't seem to get 100% CPU, but can at least get 92% using (now) either the 10 WUs at once or this:
<app_info>

<app>
<name>poemcl</name>
<user_friendly_name>POEM++ OpenCL</user_friendly_name>
</app>

<file_info>
<name>poemcl_0.1_windows_intelx86__opencl_ati_10 0</name>
<executable/>
</file_info>

<app_version>
<app_name>poemcl</app_name>
<version_num>1</version_num>
<plan_class>opencl_ati_100</plan_class>
<avg_ncpus>0.67</avg_ncpus>
<max_ncpus>4</max_ncpus>
<flops>2.1e10</flops>
<coproc>
<type>ATI</type>
<count>0.16</count>
</coproc>
<cmdline></cmdline>
<file_ref>
<file_name>poemcl_0.1_windows_intelx86__opencl_ati _100</file_name>
<main_program/>
</file_ref>
</app_version>

<app>
<name>poempp</name>
<user_friendly_name>POEM++</user_friendly_name>
</app>

<file_info>
<name>poempp_0.8_windows_intelx86</name>
<executable/>
</file_info>

<app_version>
<app_name>poempp</app_name>
<version_num>8</version_num>

<file_ref>
<file_name>poempp_0.8_windows_intelx86</file_name>
<main_program/>
</file_ref>
</app_version>
</app_info>
The extra app I added to it recently is so that I can do both CPU and GPU WUs at the same time, so that I may run 4 cores in CPU, with the other 4 cores running my 6850.

I might buy two 7970's or the dual version in next few months, I would like to see how well they perform, and hopefully a price drop soon. If they perform as well as early GPGPU benchmarks have shown, they are going to be awesome in GPU projects, once they are supported.