I've recently rebuilt my 5 yr old computer, with very good results.
As indicated by the windows performance index, my cpu/memory scores have gone up to 7.6, my graphics scores have gone up to 7.4, however:
My hard drive score remains at 5.9, which is my overall score as windows uses the lowest score for the overall score.
My question is this. I replaced the hard drive with what I thought was one of the best ones out there for my needs. A WD 1-terabyte black caviar. In the performance tests, this one runs with the best of them.
This is the same score I received on the old system with a 5 yr old wd 340 meg drive!
Hard drive access times really haven't changed much in the last decade. The transfer rates have gone up with the increased data density, but that's not as significant as access times for all-around performance.
Vista used to cap all of the performance scores at 5.9, but Windows 7 has extended the range to 7.9 to allow for newer technology such as SSDs. SSDs have WAY faster access times than hard drives (around 100 times faster!), and they usually get scores in the 7's. With a hard drive you'll have a pretty difficult time getting above 5.9 without using RAID.
If you're building a high-end system and paying for top performance, you're missing the boat if you don't at least consider an SSD.