I knew I wasn't the only one with this problem!!!
I have been fighting this since the day I got these stupid WD drives. 4 WD5000YS drives in a RAID5 on a 3ware 9650SE, any stripe size, with or without NCQ, etc ... no matter what we get about ~40-50MB/s reads and ~150-180MB/s writes. Something is horribly wrong here. I start to think it's something to do with the 3ware, then I think its the drives, then I think its the intel 5000P chipset... no idea, I just know seagates work perfectly fine. I opened case # 050207-5051842 with WD to try to get to the bottom of this - please HELP! We have like 50 of these drives and half fail (no firmware update yet) the other other half performance just sucks (firmware updated).