I just switched from a single Seagate 7200.11 500gb drive to a pair of WD 500gb Black drives configured in a Raid 0 w/ 128k stripe size. Using my onboard raid controller found on my Asus Maximus Formula mother board.
HD Tune: Intel Raid 0 Volume Benchmark
Transfer Rate Minimum : 83.9 MB/sec
Transfer Rate Maximum : 179.0 MB/sec
Transfer Rate Average : 144.3 MB/sec
Access Time : 12.6 ms
Burst Rate : 141.4 MB/sec
CPU Usage : -1.0%
These scores seem very low to me when I look at other raid benchmarks with the same or similar hard drives.