To balance the latency by adding pipeline stages, add the stage to the control path and not the data path. The data path includes wider buses, which increases the number of flip-flop and register resources used.
If you have a 128-bit data path, two stages of registers, and a requirement of five cycles of latency, consider the following. Inserting three register stages results in an extra 3 x 128 = 384 flip-flops. Alternatively, you can use registers to control logic to enable the data path. Use five stages of single-bit registers to control the enable signal of datapath flip-flops and multicycle path timing exceptions accordingly.
Note: This example is only possible for certain
designs. For example, in cases where there is a fanout from the intermediate data path
flip-flops, having only two stages does not work.
Recommended: The optimal LUT:FF
ratio in a device is 1:1. Designs with significantly more FFs increase unrelated logic
packing into slices, which increase routing complexity and can degrade QoR.