The slowest is the WD green, avaraging 90MB/S sequential write. That is one of the most used large storage drives (all the faster ones are often 1Tb or smaller) together with the Samsung Spinpoint series (missing in the test). So that quite matches the speed of FW800, and it matches my real life experience between USB3 and FW: copying the complete content for backup (many mixed size files) is only giving 5% speed difference between the two (on the small stuff FW 800 also wins some times). Reading speed is not that important, again, big drives are mostly used to store a lot, and at read (serving movies etc) throughput is not so important.
And you know what is the fastest here on my 2012 mini: reading from the USB2/3 drive and write it to the FW800 drive. If write and read are on the same bus, it is much slower.
You'll have to point to me where the WD Green drive is the most used external? About 6 months ago Seagate went to a single drive for all of their Mechanical Drives, so ALL of my externals I purchased on Black friday (all 6 of them) were the Seagate 3TB 7200 RPM drives that have a sequential read/write average of 150MB/s. Oh and Samsung mechanical drives no longer exist which is why they were absent. Seagate bought them out over a year ago.
So rather than make up statistics, please provide me with data that shows that (non-existent) Samsung drives and WD Green drives are the most purchased external drives today.
Edit: Further, the Firewire 800 would still even starve a WD Green at the fastest transfer speeds when the drive is fairly empty. It isn't until the drive is half full or better that the drive would be putting out at or below Firewire 800.