I have one of those, an ME320U2, and on my current notebook I can almost hit 15X read. It benchmarks @ 19MB/s burst.
I have no problems with 16X with this enclosure:
http://www.dealsonic.com/plpmblidetof.html on USB. The 1394 drops out on me, but the USB benchmarks @ 23MB/s and 1394 @ 26MB/s (when it's there) burst.
But... my notebook specs are: 3.2 P4 HT, 800 MHz FSB, 7200 RPM HDD W/ 8-MB cache, 1-GB RAM.
I could not come close to that transfer rate with my other notebook, maybe 11-1/2X, which was the same spec except 2.4 P4, 400 MHz FSB.
Personally, I think that the increased performance is in the faster Bus speed.
I know that I can compress video with Shrink more than twice as fast with the new notebook.
Cheers,
Blaine