Capture NX2 - Scratch disk

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I'm installing Capture NX2  on a new HP H8t desktop, 12GB memory, 1T internal hd, w/Windows 7. I will also be adding Elements 9 and Silver Efex.

Q: For best performance should I set up the scratch disk on the internal hd or on one of 2 external hard drives I have?

Q: Should I set up a separate hd partition for the scratch disk? If so, large?

Q: Same question for setting the cache & temp files? And, should they be on the same hd, same partition, or separate from the scratch disk?

Q: Regarding Element 9... Should it have it's own scratch, cache, & temp file area?

Thanks!