Here are my preliminary findings.
The Ableconn/Delock Marvell 88SA8052 does not work properly with DMA enabled on the ICH2. I tested it with two drives, one with a Linkmedia chipset and one with a Sandforce. The test platform was the ICH2 southbridge with the latest Windows 9x Intel INF installed for this platform (6.3.0.1007). I tested in both APM and ACPI mode. The symptom exhibited was that the mouse movement was slow, but I couldn't point that behavior specifically to read/write operations, since this did not happen during ATTO benchmarking, and ATTO benchmarking was perfectly fine with good numbers, despite this issue.
I then moved on to testing with a Startech IDE2SAT which uses the same Marvell chip. The chips look different though, the Ableconn has a 2021 datecode and the Startech a 2020 datecode. The Startech chip also has the Marvell logo, while the Ableconn does not, but they are both QFP and exactly the same shape, so I don't think this is really that important or pertinent. I interfaced the IDE2SAT using an "ST6006C" mSATA to SATA adapter. I booted the system, and the problem disappeared completely, and the computer ran perfectly. No more mouse choppiness, and ATTO benchmarks were up to spec.