First off, the WD Caviar SE you have is a pretty old one, where as your brother's WD Blue is on a newer gen. This will make a difference.
If you RAID0 2x F3s or even 2x WD Blue's you will notice the difference. Right now, you are comparing across generations hence why you see lower performance.
For example, the older WD Raptors are beaten by the F3s,etc today.
Also realize all RAID does is provide redundancy (RAID1,5,10) and improve throughput. It does very little to improve 4K random read/write performance.