The difference between 3 and 2.6 GHz is 400MHz, but I guess u already know that
The more powerful card the more heat, so --> the more electric cost.
I had 40-45oC with my previous green card 4670 and now I have 45-50oC with 9800. With your 6850 I wouldnt be able to use it fanless.
About disks I made a mistake, 3 hd -->25x3=75W, not 100. My ssd -->0W
Are you sure you have green disks? Then u receive not the best performance from them.
My exact cpu settings are the defaults without the turbo boost. Only when I need more power I raise to 3.5-3.9GHz with +0,5-1,2V.
Cool&Quiet of course on(auto).
Lately I see many speakers reviews, but havent found something good yet.
Usually I get advice from newegg.
Have u got a specific model for audiophiles to suggest me?