Not to beat a dead horse here, but I feel possessed to follow up the unwavering faith of some in FW800's superiority.
never understood why people go for usb other then for mouse and keyboard or a printer , if i gave you the choice between a ferrari enzo and a fiat 500 which one would you take
Same reason that people buy Fiat 500s instead of Ferraris--both get you where you want to go, but one is cheaper than the other. Heck, if you drive the speed limit, the Ferrari may not even get you there any faster, which is analogous to the backup issue being discussed here.
Similarly, to use
very general numbers as an example, a 2TB Fantom drive with FW800 will cost you about $200, while a similar USB/eSATA-only one is about $150. Depending on what you want to do with it, that $50 may not be worth the added speed, which you may never, in practice, see.
Since my home server backs up automatically in the middle of the night when I'm asleep every day (and it's data only, not bootable, so that's not an issue), I could care less whether it takes 15 minutes or 45--I'd rather have that $50 to spend on something else. It might take an extra hour to restore from backup if I ever need it, but that's not likely something I'll do more than once, and it's not something I'll be staring at while it works, so it's not worth it to me.
On the other hand, my online data drive, which I actively use every day, is FW800, because the speed boost IS worth it there, at least to me. The cumulative seconds saved over a year or two are easily worth $50.
All comes down to how you're going to use it and whether the time that will or will not be saved is worth the incremental cost to you.
Also:
... ok if you only plan to transfer small 200mb text files around then usb2.0 is sufficient ...
200MB text files? What kind of text are you slinging? I have a 424-page formatted novel manuscript here that's under 1MB, and 500K words of web text and supporting info is under 12MB.