more than 10TB
from the looks of it FIO's octal tops out at 10TB for a single card. The cost of such a card makes it worth while to have a server that has a lot of horsepower, say something like a quad socket system that has, nearly a dozen PCIe slots, e.g. DL58G7 which could get 4x10TB cards(PCIe 16x), and a few more 1-2TB cards (PCIe 8x) cards in it at the same time.
Or go bigger with an 8-way DL980 -
I would think the distinction of the fusion method is you can use pretty much any server hardware you want - even blades (in HP's case anyways since they have FIO modules for their blades), and don't need to wait for the fully integrated stacks to emerge, get the added speed now (assuming you need it - I sure as hell don't!)
Also I'd assume it's easier to get up and going with Fusion - since you can start small(160GB), and grow more later.
Though fusion certainly has a lot more competition now than a few years ago!