Hi,
Your effective "data rate" is a function of how much data you can transmit per message and how quickly you are transmitting messages. ANT burst, acknowledged and broadcast messages contain an 8-byte (64-bit) data payload. With ack and broadcast messages, the application controls the transmit rate which it might be able to set up to 200-300 Hz depending on the device, platform, bus speeds etc. Thus your maximum data rate in that case is anywhere around ~12.8-19.2 kbps.
For burst messaging, ANT controls the rate messages are transmitted at and will interrupt other active channels to do so. An ANT burst transmits at ~3ms between each message, with each message being 64 bits of payload, which yields 20 kbps. An advanced burst brings the message payload to 24-bytes (192 bits), with the time between the start of each message remaining the same, yielding 60kbps.