USB stats are based on burst speeds. Firewire is constant. The stats you mentioned are highly misleading.
USB relies on CPU power, Firewire does not.
Even Firewire 400 outperforms USB 2.0 in high-bandwidth applications such as external HDs. Considering Firewire 800 is twice as fast as 400 it totally smokes USB. There is no comparison.
You will notice a huge difference between Firewire 800 and USB 2.0 in regular usage of an external HD.
check out the burst speed of USB so you see what you said is inaccurate. Of the two test the more "steady" (and you can see this by the narrow min/max speeds) one was actually USB because the limiting factor was actually the port itself. In eSATA the speed varied considerably due to the transfer being limited by the HDD itself. Also in real life situation the access time becomes important as well, narrowing further the advantage of FW. Again FW does outperform USB but thats beside the point because it depends on what you are using the HDD for, for backup you need no lightning fast speeds specially if its more expensive. Now if you were to install applications, boot off the drive, move/copy lots of large files, or you got too much money then yes, but if you are just going to copy 50GB of music, 20GB of video and Time machine which you only do ONCE and then just bit by bit "update" your data every other day, then it makes little sense to spend all that much on extra speed.
I think i'm gonna go for either a USB or one with both. I'm not really gonna have any massive files to transfer over only really word documents and probably bits of music, so i dont really need lightning fast transfers. At the moment the Lacie is looking like the front runner.
If you going for a FW version (I would not due to what I just wrote above, but thats your choice) make sure at least its the 7200rpm HDD, as I said the 5400rpm on FW is just like 10Mbit/s faster due to it being limited by the HDD speed and not by the port (in fact unless you buy a velociraptor all HDDs will be the limiting factor for FW, the port should be able to max the HDD speed.)
I see a lot of people have recommended 3.5" drive (all of which require a DC adapter) did you change of mind on the matter? because if you did, it does worth checking eSATA/FW HDDs because those drive do can do ~100MB/s and you can get 1TB. Else I'd go for a Seagate 500gb version or WD 500Gb version.
If
these are the accurate prices for the lacie HDD, then I'd advice against them since they are expensive. $140 for a 500Gb USB alone is expensive, $250 for a USB/FW combo is a ripoff!
@DKatri OK so I just realized that your MBP got a 160GB 5400rpm, whatever the case is, I am pretty sure that HDD will be the limiting factor (or very close) and since the data you write to the external HDD must be read from the internal then thats the max speed you'd be able to transfer files. I reckon that your HDD will max at about ~40-45MB/s (mine 200GB max at 50MB/s but yours should be a couple of MBs slower due to lower density) and some of that bandwidth will be "reserved" by the system. At this point I really don't advice on anything faster unless you are planning on using the HDD in a different computer most of the time, or you are planning on upgrading your internal HDD.