caculate chunk size for the future

hi:
    I have a 4 disk software raid6. I found chunk size 512k give me
best performance for my workload.

    if I grow up the raid to 32 disks, may I assume chunk size 64K
will give me similar performance? or there will other impact when I
grow the disks in the future?

  I saw discussion about internal bitmap hit the performance for 20
disks raid10. is raid5/6 ok under the same situation?

     thanks a lot for help!

Regards,
tbskyd