Someone call the Shrimp, to make sure.
Frankly, I believe it is a case of a good controller (ICH) and a fresh drive with compressible data. If the data consists of typical IOMeter data (a repeat of 0123456789 over and over), the controller could very easily push that in a very small amount of space and need not read the actual cell content but minor auxiliary data that says the LBA is a copy of another LBA which was already read (hence in cache). 128MB cache or even 64MB would be enough to hold an 8GB IOMeter file in compressed form.
Either way the results would be pointless, but the test might be true.