If you have increased max_wal_size, it's reasonable to also increase checkpoint_competion_target to its practical maximum of 0.9. This gives maximum checkpoint spreading, which theoretically means the smoothest I/O too. In some cases, keeping the default of 0.5 will still be better, however, as it makes it less likely that one checkpoint's writes will spill into the next one.
It's unlikely a value below 0.5 will be very effective at spreading checkpoints at all, and unless you have an extremely large value for the number of segments, the practical difference between small changes in its value are unlikely to matter. One approach for the really thorough is to try both 0.5 and 0.9 with your application and see which gives the smoother disk I/O curve over time, as judged by OS-level monitoring.