MD1220 Strip Element Size and Read/Write Policies for Raid 6

I have a MD1220 with 24 - 146GB 15K sas drives.  I want to use it for storing backups of Hyper-V vm's and hosts.  These are small configurations so 1.5TB should be plenty of space. I would like to know what the optimum stripe element size and Read / Write policies would be best. My Choices are,

Stripe Element Size: 8, 16, 32, 64, 128, 256, 512KB or 1MB

Read Policy: Read Ahead, Adaptive Read Ahead, No Read ahead

Write Policy:  Write Back, Write Through, Force Write Back

Thanks