First, FireWire's max speed is 50MB/sec, which is probably why the drive you're looking at is rated at that speed. In short, you're not going to get any better than that under any circumstances (and you're not likely to actually get 50MB/sec anyway).
Second, the choice of drive is going to depend on how serious you are in your video editing. If you're a low volume user just doing video transfers then almost any external FireWire drive will suffice. If you're a professional, though, doing lots of real-time video work, effects, transitions, etc. and for whom time is money, you'd be better off with a LVD SCSI array and a SCSI Ultra160 card.
Obviously, cost is going to be a difference here.
In any case, if you're serious about FCP, get a FCP-certified drive.
Remember, virtually all external 'FireWire' drives are really ATA drives with a FireWire bridge to let them connect via FireWire.
For the professional user, I highly recommend
ProMax. They not the cheapest, but have been around forever and really know their stuff.