I agree with WR2, I'd get the 4850 with the P45 to allow a second 4850 during a sale like Black Friday or Boxing Week. Corsairs 550W or PC Power and Cooling's 610W is enough for the system with one of the 4850's, but I think I would want at least the 620 or even 750W Corsairs or PCP&P's for Crossfiring two of them. Although if you build every two years you can probs get away with the 550W.
The Coolermaster 690 case has excellent airflow as well as the 900, and it's cheaper. You can also choose to install extra fans from 80mm up to 140mm, though 120mm will be the sweet spot. The 900 will also require extra fans to maximize it's airflow potential. I like Yate Loon fans, but just do a quick read up on high CFM fans with low noise and balance according to your own noise tolerance/preference.
Definitely kick your ram down to DDR2-800. That will allow you to OC your E8400 up to 3.6Ghz w/o overclocking the memory (running 1:1). With the Zalman heatsink I'm not sure how much higher you would want to push it anyway, and you'd like not notice the difference between 3.6Ghz and 4.0Ghz.
Something is a bit fishy with those numbers. Here's a quote from page 5 of the Anandtech review. It's in fact right after the image you linked:
With two 4850s paired up in CrossFire, we once again ran into issues with our power supply. Our 1000W OCZ EliteXStream wasn't always enough for the dual-GPU setup and in Call of Duty 4 our system rebooted in the middle of our test at 2560 x 1600. Thankfully OCZ sent us a PC Power & Cooling Turbo Cool 1200W unit that is certified for use with GeForce GTX 280 SLI, and if it works on that beast, it had better work with a pair of 4850s in CrossFire.
The PCP&C unit is quite loud as we mentioned in our review, but it got the job done, we were able to run all of our benchmarks without a hiccup after swapping power supplies. Despite AMD's small-GPU strategy, power consumption on multi-GPU configurations is still just as much of a problem as it is for NVIDIA.
Yeah, that must be it, their PSU was just dying. LOL, 1200W for two cards that don't even need a second connector.
What about the P5Q, is that good enough for 4850 Crossfire, or should the OP look at x38/x48 instead? When used with two cards, the P5Q drops to x8 on both slots. I tried to figure out if that's a bottleneck or not but couldn't find out so far.
BTW, +1 for the RC-690 and the AC Freezer. A good SATA burner is SH-S203B for example.
When used with two cards, the P5Q drops to x8 on both slots. I tried to figure out if that's a bottleneck or not but couldn't find out so far.
Not so much a bottleneck but there is a slight penalty for having 2x8 PCI-e lanes (P-45) over 2x16 PCI-e lanes (X48).
Something along these lines:
More games bench marked in the Intel P45 Vs. X48 Crossfire Performance review @ http://www.tweaktown.com/articles/1472/
It's not much of difference at lower resolutions but at the higher resolutions 19x12 25x16 it's can be significant. It also seems to benefit the MIN frame rates too. Also note that review that Crysis had some atypical results but that may be due to driver issues with Crysis.
As to the P45 / X48 question... I can easily see me putting a second 4850 in there someday. However there is a pretty significant price difference between the boards. That seems like a tough call.
It would be an easier call if we knew you had a 24" 19x12 or 30" 25x16 monitor heading your way soon. For those of us at 16x12 and lower it doesnt seem to be as big an issue. A slight overclock on the video card and you've probably made up any difference. (Of course you could have OC'd the GPU on the X48 board and come out ahead - except in your bank account). It's always a balancing act between budget and performance in the CPU/GPU choices.
IMO your new system will hit that balance nicely. I think you're good to go.
As for the CF or new generation GPU upgrade - I've always been in the new gen upgrade camp for monitor resolutions of 16x12 and under. I also favor the lower model in the top end GPU class (as in 4850 vs 4870) for the higher bank for buck it gives. SLI or CF and/or top end GPUs for 19x12 and higher makes more sense.