I have several machines here and moved some video cards to do my own testing. Some interesting results:
PD8 v3022
Windows 7 32 bit, 4GB RAM, Q6600 2.4Ghz quad O/C to 3.0Ghz
5 minute HD1080 MOV file from my Canon 7D camera with simple beginning and ending titles added.
Test 1:
CPU only, all video hardware encoding turned off
"Burn BluRay" to disk folder
13minutes 32 seconds, all four Q6600 CPU's loaded to 98%+ during most of the enoding.
Test2:
CPU + 1 ATI HD5670 video card
all video GPU acceleration options turned on
"Burn BluRay" to disk folder
7minutes 35 seconds, Single one of the Q6600 CPU's loaded to 80%, other 3 CPU's at 25% load
Test3:
CPU + 2 ATI HD5670 video cards in a CROSSFIRE configuration
all video GPU acceleration options turned on
"Burn BluRay" to disk folder
7minutes 28 seconds, Single one of the Q6600 CPU's loaded to 60%, other 3 CPU's at 25% load
CONCLUSION:
At least for this test case, the addition of even a moderate level ATI card can nearly double the performance of your enodes plus free up your CPU to actually do other work during the encoding session. Using multiple ATI cards in a CROSSFIRE setup does not yield any advantage for PD8.
Possibly, with a lessor CPU, the GPU and CROSSFIRE results might change.