RE:6.9 rating dropping to 5.9, unless the new Seagate Hybrid drive they just debuted breaks the 5.9 rating in WEI the best a traditional hard drive can get is a 5.9. If you want to use an SSD in your system it's easily added.
I have 3 systems running Windows 7, the oldest is a nearly 6 y/o DELL XPS Gen 1 laptop with a 160Gb HDD and it get's a 4.8 WEI due to the video card that cannot be upgraded futher, the HDD gets a 5.9.
The second is my Alienware M17x r1, it has a 320Gb HDD and a 160Gb SSD, I load the SSD with the OS and keep all my programs and files on the HDD. It has a WEI of 7.1 with the CPU being the lowest score, the SSD is 7.5, video is 7.4. My SSD is Drive1 or the D: drive.
The third PC is my DELL Studio XPS 435T/9000, it has 2 1.5Tb internal HDD's with Vista 64, Windows Home Premium 64 and Ubuntu loaded on them, I also have a 3rd 1.5Tb as an external drive connected as eSATA and it is the network drive off this PC when it is running. The Windows 7 Ultimate 64 OS is loaded on the M: drive a 256Gb SSD and the WEI is 7.6 which is the low score on the video card an XFX 5870 XXX Edition, the SSD runs at 7.7 and CPU 7.8 (an i7 975 Extreme).
I would not let the WEI numbers bother you, if you are concerned with Benchmarks there are better ones out there to make you feel better but the reality of this is if your system performs for you the way that you expect there is no better Benchmark no matter what the numbers show.
If you do decide to go with an SSD, spend some time reading about how the different models from the manufacturers perform, they are not all equal. If you will delegate the SSD like I have which is to only run the OS then TRIM may not be a requirement since you realistically will not load anything other than OS updates. If you will use it for programs as well TRIM will be something to look at, not all of them handle garbage collection alike.
What I find invaluable is the software program Acronis True Image, this allows me to keep an image of my SSD. I alternate my image saving between the eSATA network drive and the network drive I have attached to my router which has saved me quite a bit of time reloading the SSD in both the PC and the M17x when I was experimenting, all I needed to do was format the drive, reload the OS and then re-image from Acronis giving me a full running system in very short order. Hope some of what I posted here is of assist to you, welcome to the 7 Forums.