You need to share a bit more information. Specifically:
- how much of that 2TB will you need to be "active" at one time,
- how much of a factor is money/cost?
Fastest is probably a RAID 0 made of fast(est) SSD drives. You could probably assemble a RAID 0 SSD to max out the speed of the OWC e-sata mod.
If you don't want to the e-sata mod, you could aim for maxing out Firewire 800 speeds.
Next fastest (and cheaper) would be a RAID 0 of fastest hard drives, probably of the 500Mb sizes (so 4 of them), or maybe more drives with smaller capacities. RPMs and speed of the RAID box might be the big factors here.
A cheaper answer is a fast 2TB external, or 2 (disc) 1TB Raid 0 box, but there you are trading speed for cost.
Post answers to the 2 questions above and you should get better feedback. If you have a budget max, that would guide the answers as well.