To identify most appropriated Oracle block size on given file system

To identify most appropriated Oracle block size on file system mounted to /oracle/TEST/ we tried the following tests:

oracle$ time dd if=/dev/zero of=/oracle/TEST/16K.test bs=16k count=16384
16384+0 records in
16384+0 records out
268435456 bytes (268 MB) copied, 2.64192 seconds, 102 MB/s

real    0m2.651s
user    0m0.017s
sys     0m0.223s
oracle$ time dd if=/dev/zero of=/oracle/TEST/8K.test bs=8k count=32768
32768+0 records in
32768+0 records out
268435456 bytes (268 MB) copied, 2.57524 seconds, 104 MB/s

real    0m2.578s
user    0m0.014s
sys     0m0.386s
oracle$ time dd if=/dev/zero of=/oracle/TEST/4K.test bs=4k count=65536
65536+0 records in
65536+0 records out
268435456 bytes (268 MB) copied, 2.62402 seconds, 102 MB/s

real    0m2.626s
user    0m0.005s
sys     0m0.379s