Who knows the max. data transfer rate really??

USB2.0 is 480Mbps,i.e. 60MB/s. However, there is a throughput limit on a single USB device which is seldom mentioned. I forgot the exact value. It seems to be 20MB/s. Besides, there is 10% system reserve bandwidth and overhead used for "control code". I have no idea whether it is true for the thrival read/write action over the USB-to-IDE(controler) having legacy and drawing the CPU cycle to drop the overall performance. Think about the SCSI and Ultra-DMA make use of the DMA channel to faciliate the high throughput. FYI, my USB2.0 8X DVD-writer run at 11xxx Byte/s stably.

IEEE1394a(firewire) is 400Mbps, i.e. 50MB/s. Unlike the USB standard,it was designed for DV and high transfer rate demand. The bus architecture is similar to SCSI. Is seems that no throughput limitation on IEEE1394. Of course, the overhead will draw some bandwidth, which also appeared in USB. I guess the transfer rate may be up to 40MB/s.

Well, another use of eSATA would be the HDD extention of Notebook computer or high speed DVD-writer(16x or above) in future.

Note that, the bandwidth of PC Card interface:
CardBus (32 bit burst mode)
* Byte mode: 33 Mbytes/sec
* Word mode: 66 Mbytes/sec
* DWord mode: 132 Mbytes/sec

132*8~=1056Mbit/s.

Compared with SATA1.0 1500Mbit/s, the bandwidth of CardBus interface is much less than SATA1.0 . So, we should consider this limitation when do upgrade.