i7 860 2.8GHz have lower power consumption than i7 920 2.66Ghz.
However, if you're to heavy OCing, I won't recommend you to take iy 860 2.8Ghz of course.
Take a look of my RIG at my Signature. It might help you out since you're taking many similar hardwares.

You need to think twice on choosing,
a.) i7 860(good for non-OCer or minor OCer, lower power usage, only need cheap P55 Mobo, 5% of total graphic reduction if CF/SLI using high-end GPUs which is damn little LOL, have 4 RAM slots)
b.) i7 920(good for heavy OCer, higher power usage, need expensive X58 Mobo, no graphic reduction if CF/SLI using high-end GPUs, have 6 RAM slots)

6 RAM slots(6GB or 12GB RAM) are useless for gamer, they're for Workstation people. LOL. Because 4GB of RAM is enough for any Games already.
5% Graphic Reduction means 5% of The Total Graphic Power of your CFed/SLIed GPUs. So, it's not much.
@racerx,
Good combo!

This post has been edited by DarkSilver: Dec 7 2009, 01:24 AM

You can't use Triple-Channel RAM on i7 860 + P55 MOBO.
So, you can't have 3X2GB DDR3 RAM here.
Put 2X2GB DDR3 RAM is enough for you definitely(you're not workstation people I suppose).
Good PSU choosing, so, in the future, you can CF another HD5870(if you don't plan to CF don't choose such high power PSU). But ECS A2 Black edition can support CF/SLI?

This post has been edited by DarkSilver: Dec 7 2009, 01:27 AM

Processor:Intel Core i7 860 RM1000
Motherboard: MSI P55-GD65 RM560
Ram: OCZ Gold DDR3-1066 2X2GB(4GB) RM 280
Graphic Card:Power Color HD5870 1GB GDDR5 RM 1350
Power Supply:Xigmatek 650W SLI/CF Ready 80+ RM379 or Gigabyte ODIN M 550Watt SLI/CF Ready APFC 80+ RM299(if you're not planning for CF/SLI in the future)
Casing: Cooler Master CM690 with 4 fans(I suppose it's 3 FANs only) RM265-RM280
Hdd:WD 500gb X2 raid0(get a velociraptor better?) Price I am not sure for this...

I think he don't need the DDR3-1333 RAM, just get the OCZ DDR-1066 RAM 2X2GB for RM 280 from C-Zone! Best buy!
C-Zone sell the CM690 very expensive. But that time I got no choice because very late already(lowyat gonna close), so, I accept the price. LOL.