I know this is a crazy as hell thread resurrection but maybe some others are running into these kinds of problems still. I was suffering from the exact same issue as you, But ONLY when I was in crossfire, everything was perfect with a single card. I think I only started noticing this with DX9 games (Guild Wars and Halo both did it, Skyrim didn't seem to tear, but the thing that was causing it was still observed while playing) after I installed 12.1 preview drivers.
For me the problem was the way AMD Power savings works by adjusting the GPU/Memory clocks for both video cards. One card would be running at 850mhz/1200mhz While the second one was sitting at 157mhz/300mhz, or between that and 600/900mhz, right in the middle of a gaming session. I'm assuming that really screws with settings like Vsync so thats why even with Vsync enabled it seemed to make no difference on or off.
NOTE: Pretty sure doing this method voids the warranty, just a note
So to keep both cards running at a constant 850/1200mhz I used the method of editing the .xml Profile: (Win7)
C:\Users\YourUsername\AppData\Local\ATI\ACE\
1. Right click Profiles and open it with Notepad ( You may want to Copy/paste the original profile to the Desktop in case you find that this doesn't work for your system )
2. CTRL+F search for: ForceHigh3DClocks
<Feature name="ForceHigh3DClocks">
<Property name="ForceHigh3DClocks" value="Disable">
-Type Enable in place of Disable.
-Repeat this again for the second card: Find next ForceHigh3DClocks, Enable in place of Disable
3. These values depend on what kind of card you have, but if you have a 5870 it should be Identical to mine.
-CTRL+F search again for: OverclockEnabledProperty
These are the settings I used. I referenced the highest values ("Want_2") from CoreClockTarget_1, MemoryClockTarget_1, and CoreVoltageTarget_1 to get the values for Want_0 and Want_1 of the rest. I would leave the MemoryVoltageTarget's at 0.
<Feature name="OverclockEnabled">
<Property name="OverclockEnabledProperty" value="False" />
</Feature>
<Feature name="CoreClockTarget_0">
<Property name="Want_0" value="0" /> ~ Changed to 85000
<Property name="Want_1" value="0" /> ~ Changed to 85000
<Property name="Want_2" value="85000" />
</Feature>
<Feature name="MemoryClockTarget_0">
<Property name="Want_0" value="0" /> ~ Changed to 120000
<Property name="Want_1" value="0" /> ~ Changed to 120000
<Property name="Want_2" value="120000" />
</Feature>
<Feature name="CoreVoltageTarget_0">
<Property name="Want_0" value="0" /> ~ Changed to 1163
<Property name="Want_1" value="0" /> ~ Changed to 1163
<Property name="Want_2" value="0" /> ~ Changed to 1163
</Feature>
<Feature name="MemoryVoltageTarget_0"> Left these at 0
<Property name="Want_0" value="0" />
<Property name="Want_1" value="0" />
<Property name="Want_2" value="0" />
</Feature>
<Feature name="FanSpeedProtocol_0">
<Property name="FanSpeedProtocolProperty" value="RPM" />
</Feature>
<Feature name="FanSpeedAlgorithm_0">
<Property name="FanSpeedAlgorithm" value="Automatic" />
</Feature>
<Feature name="FanSpeedRPMTarget_0">
<Property name="Want" value="0" />
</Feature>
<Feature name="FanSpeedPercentTarget_0">
<Property name="Want" value="0" />
</Feature>
<Feature name="CoreClockTarget_1">
<Property name="Want_0" value="15700" /> ~ Changed to 85000
<Property name="Want_1" value="60000" /> ~ Changed to 85000
<Property name="Want_2" value="85000" /> - Referenced
</Feature>
<Feature name="MemoryClockTarget_1">
<Property name="Want_0" value="30000" /> ~ Changed to 120000
<Property name="Want_1" value="90000" /> ~ Changed to 120000
<Property name="Want_2" value="120000" /> - Referenced
</Feature>
<Feature name="CoreVoltageTarget_1">
<Property name="Want_0" value="950" /> ~ Changed to 1163
<Property name="Want_1" value="1063" /> ~ Changed to 1163
<Property name="Want_2" value="1163" /> ~ Referenced
</Feature>
<Feature name="MemoryVoltageTarget_1"> Also left at 0
<Property name="Want_0" value="0" />
<Property name="Want_1" value="0" />
<Property name="Want_2" value="0" />
</Feature>
<Feature name="FanSpeedProtocol_1">
<Property name="FanSpeedProtocolProperty" value="Percent" />
</Feature>
<Feature name="FanSpeedAlgorithm_1">
<Property name="FanSpeedAlgorithm" value="Automatic" />
</Feature>
<Feature name="FanSpeedRPMTarget_1">
<Property name="Want" value="1246" />
</Feature>
<Feature name="FanSpeedPercentTarget_1">
<Property name="Want" value="50" />
4. Open up Task manager and close CCC.exe and MOM.exe ( Windows might say the programs not working properly, click cancel if it asks to search for a solution) then Save As the Profiles document, Navigate to the ATI folder and save it over the previous one. You might have to have windows display All file types to see the original .xml document.
5. Restart, Open up CCC, Enable AMD Overdrive. If you want to shut off the forced clock settings just disable Overdrive. It'll go back to power saving modes until you turn it on again. Hope this helps!
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