You have covered the options that I am aware of.
My 2¢ on these external drives based on a small amount of experience using the FireStore is:
Be sure you really need one!
Yes, they save you time capturing to computer but they give you more bits to carry around as you shoot and the 4 pin firewire connector to the camera is not robust enough for continuous use.
I would rather have an in-camera solution such as tape, P2 cards or equivalent.
If you are in the market for a lightly-used 40 Gig Firestore, please contact me!