How should I configure these disks on a SQL Server for a BI configuration?
2 * 10k RAID1 for OS, 6 * 15k RAID10 for everything else. Honestly, with this many disks 1 array is the safest and usually fastest bet.

If you've got time to test and have a real world, repeatable, measurable workload then by all means do a test run with your tempdb on the OS drive (caveat: limit tempdb file growth to ensure you don't splat the OS). Flip side, you may see moderate improvements to your data load and maintenance with the log there instead so worth a test run or two if time permits.