What is the maximum achievable data rate for this wireless modem?The max available bandwidth per time slot in GPRS is 21.4kbps.
The following two paragraphs apply to the download speed only.
Our modems are Class 10, which allows up to 4 time slots for download or 85.6kbps total. Due to error correction and other overhead, the actual measured speed is about half of the theoretical. I have seen 50k, but 40k is more typical. High network traffic will reduce speed even more.
Another factor that affects speed is the carrier. Some carriers support only Class 2, which allows up to 2 time slots for download. For those carriers, the data rate will be half of the speed of Class 10. That makes the typical speed about 20kbps.
For upload, typically one time slot is allowed, so you can expect about 10kbps for upload speed.