I got the best performance by creating multiple mirrorsets instead of one big RAID 10 set (Mirrored stripes). I created a filegroup made up of a file on each Windows drive (one per mirrorset).

I found that the Average disk queue length did best when Windows was throwing I/O at multiple Windows drives. The RAID array handled the I/O fine with either one big drive or multiple small ones, but Windows choked on a sinepl large drive (Avg. Disk Queue Lengths approaching 900 - the recommended target is 5). Looks like Windows I/O subsystem is the bottleneck (which any unix Admin will tell you).