I have 2 Bytecc dual-link cases. One is Oxford and the other is Prolific. The Oxford will do 16x burns and reads on Firewire, and 12x on USB2. I haven't really tested the Prolific with optical, maybe I'll do that.
Here they are, daisy-chained. The oxford has a Seagate HD in it, which benchmarks at around 30MB/sec sustained on Firewire, 20MB/sec on USB2.