In general I agree with these suggestions, but there are a couple of things I would do differently.
They talk about a quad core with HT. That means i7. I would definitely suggest a X58 mobo and thus i7-9xx CPU, especially since they emphasize - quite correctly - the importance of having a raid configuration and a P55 mobo has no expansion capability to add a PCIe raid controller. So an i7-860 is not a good option IMO.
When we talk about an i7-9xx CPU, we talk about minimum of 6 GB and much better 12 GB of Ram, or even 24 when it gets more affordable.
Bill and I have seen significant performance gains by going from 6 to 12 GB Ram.
It can't be said often enough, but when you have a decent system under CS4 and upgrade to CS5 and a CUDA / MPE card, the video card will be a significant boost in performance, and because the CPU has less work to do (that is being handled by MPE), it can do the remaining tasks more efficiently and faster. However if the disk setup is not improved at the same time, that will be the new bottleneck in this system. Optimizing for MPE means a closer look at the disk setup and Lynda.com rightly draws our attention to that fact.
"However if the disk setup is not improved at the same time, that will be the new bottleneck in this system."
This is what we experienced while editing the four screen monster that played last week in Miami. The hard drives without Raid simply were not fast enough to play some segments of the timeline. We could move the CTI over a spot that had 3840 x 540 footage in the QuickTime Animation codec sped up to 500% and see the timeline image freeze in the Program Monitor for as long as 30 seconds. We made do with what we had though, but could have really benefited from a good raid setup.