hello. Can you tell which device is generating the interrupts and where the interrupts are being routed? When I've seen things like this in the past, I've found the issue is often that the interrupts aren't getting to the right driver, or they're going to no driver, which creates a lot of CPU overhead. Are you geting missed interrupt messages from the kernel for the SATA chips? That's a sign interrupt routing is an issue. Just out of curiosity, what happens if you boot with ACPI disabled on this machine?
-thanks -Brian
