USB 2.0 to eSATA adapter speeds?

I am trying to figure out the best way to connect and audio interface to my Thinkpad.
There are several ways, but have narrowed down my options, which brings me to my questions, having to do with said options.

I have am convinced that I should use the expresscard port for the connection because of the direct connection to the mother board, essentially skipping the FSB (i think) . Either way, it would be, and is the fastest connection I currently have available.

My question is this. Are the USB2.0 to eSATA adapters any good. Is there a significant loss of speed? I can see no reason for any with the exception that the card may transfer data in USB mode rather than eSATA mode. (something I have never quite understood...is there an option somewhere?) Still, pcie transferring in USB is far faster than simple USB 2.0

Not only would this be great for an Audio Interface, but for the terabytes of USB 2.0 storage I have.
My last question is about firewire. If I were to do the same thing with firewire, would it make a difference.
I could either buy a Firewire expresscard: if that would be faster than the Firewire 400 port I have, or I could buy a firewire to eSATA adapter.

Is there a bottleneck at the USB connection into the audio interface, and or the External HDD, or is the bottleneck solely at and within the computer?

Perhaps a strange questions, thanks for bearing with me.

If it matters...
Win7, F16, U. Studio 11.04
Thinkpad T61
Intel Core2 Duo
4gb RAM
WD SATA II 5400 250gb