Western Digital 640GB WD6400AAKS
nVidia Geforce7050/nForce710i chipset w/AHCI enabled in BIOS, nVidia SATA-IDE v10.3.0.21 driver with NCQ enabled:
One instance: 112MB/s
Two instances (0%, 50%, 256K block)
1st instance: 112MB/s peak
2nd instance: 93MB/s peak
Graph line hops up and down like the screenshots you just posted. Average jumps around all over the place so taking the number that's displayed when 1 minute is up isn't so useful (it changes signficiantly depending on whether that particular instance is currently at peak while the other is not). Would probably have to run the benchmark for much longer for the averages to smooth out. But I'm just going to assume that with 2 instances, the average is roughly half of peak for each instance.
So it looks like we can add the WD6400AAKS to the list of drives with proper NCQ implementation.
PS My first test run was in a different system with nForce4 chipset, which apparently does not support NCQ even if it is enabled in the driver.