Windows Disk Defragmenter gets the stress test

Don't expect any test results for a few days, because this is what the Windows XP Disk Defragmenter (WDD) is having to deal with: 75% full hard drive with a lot of fragmented files, both large and small, including big compressed files with lots of fragments.
The test PC has been set up to look like a home PC that hasn't seen a defrag in its life before. This isn't too far off the mark. Since WDD is supplied with WinXP, it gets to go first. Then I will move on to Vista's built-in defrag utility, and take a peek at the Windows 7 version.
There is no time limit on how long the defrag will run. The goal is better performance, since most people leave the defrag running overnight or when they are out.
Update Sunday 1 March: As I start noting the results of the benchmarks, I have coined the term "the slouch factor" to describe what happens when a hard drive gets full. We've all noticed how a Windows machine usually feels slower after a long time of use, and as the drive gets full. There is an explanation for this, best described by Robert Ferraro of DiskTrix, in the "Hard Drive Performance Theory" section of the UltimateDefrag help file.
You can see it in the graph above: data transfer rates drop from 76MB/sec down to around 40MB/sec as you move from the start of the drive to the end. When I ran my previous Defrag Shootout, I was using a drive that had two partitions, courtesy of Acer. The first (and therefore faster) partition had the OS and temporary file space, while the second had data files. It seems that Acer was being clever by doing this, because the slouch factor is caused by the position of working (or temporary) files. When there is free space near the start of the drive, the temporary files can be manipulated there, with faster seek times and data transfer rates.
As the drive fills up and is kept "tidy" by a traditional defrag program like WDD, the position of the available free space gradually moves towards the slow end of the drive, affecting the seek time and transfer rates of new and temporary files. The computer starts to slouch, hence the slouch factor.