Even if I agree with Kraynor about WEI being worthless, I can still be a symptom of something being wrong. I wouldn't have worried about a 5.6 or even a 5.5, but scoring 5.0 when you should have got a 5.7 could mean something.
First make sure your CPU runs at the right speed (333MHz FSB + x9 multiplier = ~3GHz or, if idle, 333MHz FSB + x6 multiplier = ~2GHz). I know some older MB used to sometime default to lower FSB if some events occured, for example, if yours was to default to FSB 266 (1066), your CPU yould run at 2.4GHz top.
Also check that there were no CPU hungry application running in the background like a Virus scanner running a first full system scan for the first time or a Windows Update installing stuff. Just basic IM or live scanner shouldn't matter.
I checked the bios multiplier / fsb speed and ever seemed ok.
I then upgraded the bios to the latest 0402 version (came out on 21/03/2008) and after doing this I noticed the multiplier was set to x6. Changing this back to x9 seems to have fixed the problem and I'm now getting 5.7 in the WEI.