Is a SATA interface in IDE mode (UDMA/133 speed) limiting for a regular 7200 RPM 1 TB HDD when compared to SATA 6 GBit/s? I once ran AIDA64 Random Read on both XP x86 with the former and 7 x64 with the latter (with AMD AHCI drivers installed), and found the XP configuration to actually score slightly higher, despite NCQ and the other obvious advantages that AHCI offers.
AHCI certainly gets around that damn UltraDMA PIO fallback problem with emulating SATA drives on ATA controllers.
AHCI allows for Native Command Queuing, which is a bit of a speed boost and hot plugging of drives. I have never tested the throughput on any of my WD Black 1TB SATAIII drives, but it likely is a bottleneck using PATA. That being said, if your choice is a PCI card with known quirky first gen SATA150 chipsets or using a PATA adapter, I would go with the latter. The PCI bus limits throughput anyway and the cards are way more hassle than its worth if they don't work 100% with the drive.
The newest generation of drives can touch 200MB/sec on the inner tracks, so they would be somewhat limited by ATA/133 speed. But in general use it's actually pretty uncommon to peg out the transfer rate on a hard drive anyhow, so it's not likely that you'd even notice a difference unless you're dumping huge contigious files back and forth between drives constantly.
But it also depends what sort of interface you're using. A PCI SATA card will realistically only hit 90-100MB/sec at best, because there's only 133MB/sec total bandwidth to go around between all the PCI devices, and there's a certain amount of bus overhead too. If you're using an IDE->SATA converter, the speed will likely be limited even further... I wouldn't expect more than 50-60MB/sec out of those things.
IDE mode on a native SATA controller, OTOH, doesn't really have much of a speed disadvantage at all. While it's limited to the IDE command set, it's not limited to IDE speeds... a SATA/300 controller in IDE mode will still be able to do 300MB/sec (theoretically, anyway). NCQ and such really only show significant benefits on SSDs.
I was not aware of IDE emulation on SATA being capable of such high speed. For my drive device manager reports UDMA-6 as being active, so I figured it'd be limited to 133 MB/s as defined in that standard.
