External Express card GPU for laptops some questions and some answers

I just tried a Radeon 4870 connected to an old Dell D830 laptop (2GHz Core 2 duo 2Gb RAM windows XP) to see how massive the bottleneck is using the express card slot. 1st test I did was to play Skyrim and it plays perfectly on the default low settings but not playable on medium. Could this be due to the CPU bottleneck or 100% from the graphics card being crippled? I plan to try Metro 2033 tomorrow what other useful tests should I try.
I am going to sleep now but plan to try it some more tomorrow and post some numbers. What is a good way to benchmark Skyrim (and Metro) should I just run FRAPS and run round a bit killing some stuff or is there a more scientific way?

Also note this has the following limitations:
You need a standard PC power supply running externally
You can only use an external monitor (for some reason the laptop screen does not come on at all with this connected)
I think the Express card slot has a similar bandwidth as a single PCIE version 1 lane.

Thanks in advance for any useful comments like I said sleeping now so will check for them tomorrow.
 
In case anyone is interested, I just played Metro 2033 on high and it seemed very playable but Fraps said it was only average 11 FPS but it didn't record for very long so I will try again.