That depends on your CPU and which project your running on the GPUs. If you're going to fill every PCI slot with one of these, then you may need to question your power supply as well. These 430's don't use much power, but a bunch of them together may push the standard low-end power supplies to their limit.
You will probably find that not crunching any CPU tasks, allowing it to feed the GPUs only, will give you the best results. And credit-wise this is the best plan too, since the 430's will do much more work than your CPU.