I have never used T-mobiles GPRS service, but I have used Cingular's EDGE/GPRS service.

I have used the SE GC82 and the V551 via bluetooth in my Dell I8600. Both are EDGE enabled (which I assume that you know is faster than GPRS). The phone via bluetooth will transfer at 40-55 down in GPRS (using DSLRPORTS tools). In EDGE areas it will give 130 download. I never tested the GC82 speed but it did seem to load a lot quicker. The PC card uses four channels to transfer data, where the V551 uses only two channels. The PC card should be about 200.

I doubt this helps you out much because I am using a different provider and with a different card, but it may give you an idea.

Reading up on the card on SE's website it says that the max speed is 56. If you have a phone with bluetooth and a bluetooth card you may be able to save yourself some money on the card and just use your phone to access the internet. But don't forget that if you do this, you will still have to get a laptop data package.