MBP, esata and expresscard/34 slot

I have a MacBook Pro and I have just ordered an external hard disk which will have an esata interface as well as USB 2.0.

I know that esata can be a lot faster than USB 2.0 but I remember reading (unfortunately I cannot find where I saw it) that the expresscard/34 slot in the MBP has a USB2.0 data interface rather than PCI Express.

Is this true? If so, presumably there would be little benefit in buying an esata expresscard to connect to my external drive rather than just using USB.

Am I correct in this or have I misunderstood something (which is perfectly likely)?

The ExpressCard slot is connected by both USB 2.0 and PCIe (1 lane... whatever that means).

http://developer.apple.com/documentation/HardwareDrivers/Conceptual/15inMacBookPro_0706/index.html

"1 lane" refers to the number of serial links in the connection. a 1 lane connection (expresscard, pci-e x1) has 1, a pci-e x2 slot has, 2, etc.

Each "lane" supports data transfer rates of 250MB/s and is bi-directional. Thus, an expresscard slot supports a maximum bandwidth of ~500MB/s, theoretically speaking. How close to that maximum it can actually get in the real world, I don't know offhand.