I'd stick with the 10600, since that's what all the other DIMMs will be.

Working with large images in Photoshop, faster RAM will improve performance (slightly, just as it improves game performance slightly), but you'd have to have it all the faster speed. I'd not bother (even though I did bother when upgrading my system from 16 to 32 gig, I replace all the RAM with faster--I had a buyer for the old stuff though).
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Pioneer VSX-1018AH-K, PDP-5020FD, DV-79AVi
Axiom M22s, VP150, QS8s
Sony PS3, surround backs
-Chris