There's a video in the other thread that shows a speed test. These are very fast. They use the TB bandwidth and are much faster than FW800.
Either that, or the benchmarks are bad.
Just take a look at the benches and you may want one. However, they aren't cheap.
As a matter of fact, if these drives are performing like these benches indicate, they will suit my needs perfectly, so the premium is totally worth it. When I first saw the huge markup for these I was astonished at the audacity of Lacie. I just ordered one though.
Having said that, Raid implementations in my experience are not optimal, and are slow at some tasks.