dual core and ddr3??only I7 procesors benefit from triple channel>>also,less money for the case and more for your main components, you have a good idea of what you want but there isnt any build that cant be improve, 775 socket is almost dead, and your upgrade path is going to be replaced by new 1366 socket, I think you better of with Phenom II, i have the 955 and its a beast, as good as the q9550, if not better. how about this:
The build looks solid to me. I would recommend spending a bit more on the CPU cooler though, that one is ok, but not for overclocking. For socket 775, the zalmans are pretty nice (cnps 9700) but a bit pricey, and Zigmatek has some nice ones in the $40 price range.
Since you're not building for a couple months, I'd put the paper build on hold and wait till i5 gets released. Prices will change a lot when it does come out, both on the AMD and intel side. With the budget you have, you are going to get WAY more computer than you need for WoW and HTPC apps. You should be getting at least a tri core if not a quad anyway if you are going to CF or SLI (which is an option if you get an i5 system.)
If you are going to move forward with this build though, 850w PSU is overkill. 4890 CF will do fine on a 600w corsair, so to be safe, the 750 would be a good match for you.
Before I picked up an E8500, I would take a good look at AMD Phenom IIs. Reason is the upgrade path is there in the future if you need it where, as mentioned, the Core 2 is end of life.
+1 to the Xigimech HSF
Mobo will follow the CPU choosen and I'd vote you pick a different platform.
There's cheaper 4gig dual channel DDR3 kits that are Cas 7 with 7-7-7-18 timings. GSkill or Curcial I think.
The 4890 is a great card. You'll have no prob destroying WoW for the next decade with that. So unless there are other FPS games you play, I wouldn't worry to much about CF. That being said, the GTX 275 is also a great card in that price range. If you i5, then you have the option to SLI.