EDIT: Okay, so I've no idea what caused the change, but after trying loads of different things to work out what was wrong, I've rerun the WEI (about the 4th time in total) and the score has jumped to a far more respectable 7.3. I'm going to leave well alone now :)

I've got a brand new 256GB SSD (Crucial CT256M225) which should have stellar performance. However, on my (also brand new) Dell Studio 1557 with Windows 7 Professional 64 bit, it's only giving a performance index of 5.9. I realise the performance index should be taken with a bit of a pinch of salt, but I wonder whether something's wrong. Given this paragraph from this MSDN article on Windows 7, I'd expect to see a high 6.X or possible a 7.X figure:

In Windows 7, there are new random read, random write and flush assessments. Better SSDs can score above 6.5 all the way to 7.9. To be included in that range, an SSD has to have outstanding random read rates and be resilient to flush and random write workloads.

In the Beta timeframe of Windows 7, there was a capping of scores at 1.9, 2.9 or the like if a disk (SSD or HDD) didn’t perform adequately when confronted with our random write and flush assessments. Feedback on this was pretty consistent, with most feeling the level of capping to be excessive. As a result, we now simply restrict SSDs with performance issues from joining the newly added 6.0+ and 7.0+ ranges. SSDs that are not solid performers across all assessments effectively get scored in a manner similar to what they would have been in Windows Vista, gaining no Win7 boost for great random read performance.

How can I diagnose any performance issues with either the disk or how Windows 7 is handling it? Are there any particularly good tools you'd recommend?

One note of curiosity: I couldn't install the firmware update (to 1916) until I changed my BIOS handling of the drive to ATA mode; after installing the firmware I tried to boot the Windows installation DVD - but that only worked after turning it back to AHCI mode (which I've left it in).

Installing Windows 7 took longer than I expected - it sat at the "Windows is loading files" prompt for a very long time. Likewise it was on "Expanding files (0%)" for a long time. Since installation it's been fine though - but I don't know whether it's really providing quite as beefy performance as it should.

EDIT: My netbook with the 64GB equivalent drive has a performance index of 6.6...