It all depends on your use case. In my experience, most of the times when dealing with RB:s, it's more important to guarantee that the read index and the write

It all depends on your use case. In my experience, most of the times when dealing with RB:s, it's more important to guarantee that the read index and the write index can be updated lock-free by different threads (e.g. one producer and one consumer) than to have a very specific non-power-of-2 capacity.