I agree with a lot of the above.
What I would add is info about noise. Are you sure that you are not that bothered ??? Have a listen to a few different machines to see what you think is an acceptable level. If you are able to, get a listen to a recent Dell. Most people here have machines that are quieter than Dells, but if you do not pay attention to the components going into your machine you will end up with something a lot louder than a Dell most likely.
Imo RAID 0 is not worth the effort. There have been several performance tests done by high profile reviews sites, and there is next to no difference in performance. You just have to endure the hassle of setting them up, and sorting them out if they go wrong.
This is SPCR, so this will be no surprise to you. But I'm watching the TV now at low volume. I'm sitting next to both of my machines that currently have their cases off, and I cannot hear them. Only in the most quiet dialogue can I detect that they are on. The extra expense to create this bliss is less than £100 over a standard machine (as long as you consider your components from the start).
As for HDDs, these are useful for reducing the noise from Raptors and the like, see there is still hope of a fast quiet machine. Of course, one of those with a slower drive is even better in terms of noise