Hi,
Bit rate can be very low also for a high frequency carrier signal. This problem is often experienced by satellite communications engineers especially deep space flights, where data rates go down to 1bps. The mission had very low data rates, due to link margin considerations.
I would suggest you take a look at the how the Link margin are the real issues while deciding a bit rate. The implementation issues don't really bog the designer, when it comes to low data rates over high frequency bands like UHF bands.
Also, when it comes to symbol rate(and thereby the data rate) that has to do with the modulation scheme used.