So I found a solution in the end.
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.
Thanks for the help