As previously reported, we know that the the PlayStation 3 Slim uses half the power of its 'Fat' counterpart.
Now reports are coming out of the popular Japanese blog Ore-teki (linked above) that the PS3 Slim may actually be slower than its bulky predecessor.
Of course these differences may be caused by differences in harddrive, but in this case the maker of the video claims the same 7200RPM HDD is installed in each... which leaves room for firmware/hardware variations or simply random fluctuations.
Whatever the cause, it seems unlikely Sony will be admitting any undocumented performance difference between the models.
Below are some PS3 HDD and Blu-ray speed comparison videos demonstrating the apparent differences:
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