Hi jagooch and welcome to Windows 7 Forums
You will be fine with the recommended allocation unit size. The array will be formatted with the NTFS file system which is more efficient than the older FAT/FAT32 systems that were used in older OSes. With the older file system, as the size of the disk increased so did the allocation unit size because there was only a finite number of units that could be recorded in the allocation table. With NTFS, that limitation no longer exists (rather, it does, but it is way in excess of the size of HDDs that are available). As a result, NTFS allows you to use the space on the disk more effectively.