The max theoretical speed for that connection would be around 77KB/s, but I would say getting something in the 60KB/s range, or around 600Kbps (note the case of the "B" which is significant here) is pretty reasonable for a connection like that.

As you already know, it may go up or down a bit based on a large number of factors, but so long as the figures you're getting seem to be in the ballpark of 600Kbps or 60KB/s, I wouldn't worry too much about it. If you were getting 200 or 400Kbps results, that would be worth investigating.