For anyone having lag issues while running the GPU tasks I'm making no guarantees but hopefully this will help.
If you want to try this you will not be able to run WCG CPU and GPU tasks at the same time. You should be able to run CPU tasks from other BOINC projects like SIMAP or Docking but that's for a later discussion.

For Nvidia cards use this.


<app_info>
<app>
<name>hcc1</name>
<user_friendly_name>Help Conquer Cancer</user_friendly_name>
</app>
<file_info>
<name>wcg_hcc1_img_6.56_windows_intelx86__nvidia_hcc1</name>
<executable/>
</file_info>
<file_info>
<name>hcckernel.cl.6.56</name>
<executable/>
</file_info>
<app_version>
<app_name>hcc1</app_name>
<version_num>656</version_num>
<platform>windows_intelx86</platform>
<plan_class>nvidia_hcc1</plan_class>
<avg_ncpus>1.0</avg_ncpus>
<max_ncpus>1.0</max_ncpus>
<coproc>
<type>CUDA</type>
<count>1</count>
<cmdline>--gpu-target-frequency 30 --gpu-polling-mode 8 --process-priority 1</cmdline>
</coproc>
<file_ref>
<file_name>wcg_hcc1_img_6.56_windows_intelx86__nvidia_hcc1</file_name>
<main_program/>
</file_ref>
<file_ref>
<file_name>hcckernel.cl.6.56</file_name>
<open_name>hcckernel.cl</open_name>
</file_ref>
</app_version>
</app_info>



For ATI cards use this.

<app_info>
<app>
<name>hcc1</name>
<user_friendly_name>Help Conquer Cancer</user_friendly_name>
</app>
<file_info>
<name>wcg_hcc1_img_6.56_windows_intelx86__ati_hcc1</name>
<executable/>
</file_info>
<file_info>
<name>hcckernel.cl.6.56</name>
<executable/>
</file_info>
<app_version>
<app_name>hcc1</app_name>
<version_num>656</version_num>
<platform>windows_intelx86</platform>
<plan_class>ati_hcc1</plan_class>
<avg_ncpus>1.0</avg_ncpus>
<max_ncpus>1.0</max_ncpus>
<coproc>
<type>ATI</type>
<count>1</count>
<cmdline>--gpu-target-frequency 30 --gpu-polling-mode 8 --process-priority 1</cmdline>
</coproc>
<file_ref>
<file_name>wcg_hcc1_img_6.56_windows_intelx86__ati_hcc1</file_name>
<main_program/>
</file_ref>
<file_ref>
<file_name>hcckernel.cl.6.56</file_name>
<open_name>hcckernel.cl</open_name>
</file_ref>
</app_version>
</app_info>

Please read all the instructions carefully before starting and a word of caution. The following procedures will probably cause you to lose any GPU work that you have in your cache. That's nothing to worry about. Boinc will download new tasks when restarted. Don't complete all your tasks in your cache before trying this. The file needs to see at least 1 task to get info from the file.


First, copy and paste which ever file you need into a text document.
Next, rename the file app_info.xml
Next, shut down boinc.
Place the new file in the WCG project folder. To find the correct folder you must have your OS set to show hidden files and folders.
Once you have your OS set to show the hidden files/folders you can find the WCG project folder in:
XP: open My Computer, double click on main drive(usually C drive) then go to Documents and Settings>All Users>Application Data>BOINC>projects>www.worldcommunitygrid.org. Place the file in the WCG folder then close everything and restart boinc.

Win7:Open My Computer, double click on main drive (usually C drive) then go to ProgramData>BOINC>projects>www.worldcommunitygrid.org. Place the file in the WCG folder then close everything and restart boinc.

The key components of this file are the numbers 30 and 8 in the cmdline string. That string will lower the % of the GPU being use which should help the lag issues. They can be adjusted up or down if needed but they shouldn't have to be changed. Here are general instructions that may help.
(--gpu-target-frequency 30(default 30; higher number = smaller chunks)
--gpu-polling-mode 8 (default 1; ms between polling for results from gpu; higher number= longer delay in ms.)
--process-priority 1 (default 2 (normal), 0 (lowest) ... 4 (highest); process prio in windows)
Higher target frequency means the data is getting split into more chunks and in between the chunks the gpu can do something else like refreshing your screen, but in summary more time is spent on moving data to/from gpu.
Lower polling mode leads to a more busy cpu on some systems (like mine) but faster loading of the gpu with the next chunk of data.
The trick is to find the best combination of target frequency and polling mode for your system. Different size WUs can make that even more tricky.)

If you want to play with the settings shut down boinc and go to where the file is located (as per the instructions above) but do not remove the file from the WCG folder while you edit it. Right click on the app_info.xml file and open with notepad. Change the numbers as you wish but keep them even numbers except process priority. When done close the file. You'll be asked to save changes select yes. Restart boinc and see what you have.

These files were adapted from files used here to run multiple GPU tasks and a file I used when running Milkyway and had severe lag issues. I have not tested them on WCG but they should work. If you have any problems I'll do my best to help. If the file stops the GPU tasks from running or you get errors you didn't see before just go back and remove the file from the WCG folder and let me know.

One other option is to use a second card for your monitor, exclude it from crunching, and use the other only to crunch, You can do this by adding an exclude command to cc_config.xml file. You can find that in the BOINC folder.(Not in the project folder.) If you don't have a cc_config.xml file in your BOINC folder do this. Copy and paste the code below into a text file and rename it cc_config.xml. Close boinc, drop it into the BOINC folder and restart boinc.

<cc_config>
<options>
<exclude_gpu>
<url>http://www.worldcommunitygrid.org</url>
<device_num>1</device_num> <---decide which device you want to exclude. Could be gpu 0 or 1
<type>nvidia</type> <---change type to ati if you have an ati card.
<app>hcc1</app>
</exclude_gpu>
</options>
</cc_config>

If you already have a cc_config file in your BOINC folder right click on it, open with notepad. Copy and paste only the parts of the file from <options> to </options> into config file. Close and save then restart boinc. When you start boinc you should see something like this in the startup messages.

10/13/2012 9:25:37 AM | | NVIDIA GPU 0: GeForce GTX 275
10/13/2012 9:25:37 AM | | NVIDIA GPU 1 (not used): GeForce 9800 GT
10/13/2012 9:25:37 AM | | OpenCL: NVIDIA GPU 0: GeForce GTX 275
10/13/2012 9:25:37 AM | | OpenCL: NVIDIA GPU 1 (not used): GeForce 9800 GT

Hope this helps.