As I understand it, you have some inquiries related to a XCVR data rate within the same bank. In general, the number of data rates can be supported within the same bank would be dependent on the number of TX PLL ie CMU PLL, ATX PLL available for the XCVR bank. For example, if there are two CMU PLLs, then you can run XCVR at two different data rate.
Note that the above are general understanding. Would you mind to further elaborate on the specific data rate that you are planning to run and also the device that you are using?
You may also create simple test design and run through Fitter to check on the implementation.