What should the raid block size be set on a promise 4 X 2 Terrabyte Promise raid?

I posted this in the FCP section but only now realized that I should have posted it in this section

I have just recently purchased an iMac 3.4 GHz Intel Core i7 with 16 gigs of ram and a 4 X 2 terabyte promise thunderbolt raid.

What is the optimum RAID block size for editing in FCP 7 and FCP X? It is currently set as a raid 1 and the block size is set at 32K. Should I leave it at this or change it to a different setting? It is set up as a Mirrored RAID set.

If I do change it will it affect any footage I have already on the drive?

I have searched for information on this site but there is no information specific to thunderbolt drives.

Thanks

Mick
http://WWW.bogdogfilms.com