We have observed that the JTAG virtual cable server is reliable and works well. We also noted that the data rate over the JTAG chain is fixed at 10MHz. The Xilinx programming software provides an option for users to set the desired frequency and the IPMC XVC server responds to this command, but the clock frequency never changes.
For imperfect signal environments, where signal integrity may involve compromises, it would be beneficial to allow users to slow down the JTAG programming chain to avoid marginal behavior while programming at 10MHz.