If I remember correctly, bluetooth tethering will cap you to 120 KBps (that's kilobytes per second). Usually your network should be able to max that out, but as you haven't given any metrics it's pretty hard to tell.

Would it be possible for you to run some bandwidth tests, and see from there? Also, what kind of connection are we talking about? GPRS? EDGE? 3G?

I'm afraid we'll require a bit more information if you actually want opinions on the matter.