I recently used DUET to boot Win10 from a PCIex4 card on an Intel 965 chipset LGA775 motherboard with a legacy BIOS and no EFI. It gets close to the rated 2 GB/s one would expect for PCI 2.0. Woot! Very nice for a motherboard whose SATA tops out at level II, and IDE at 130MB/s. Then, greedly, I did the same on a G41 board that only had a spare PCIex1 slot. Still, close to 400 GB/s on that board, with a G41 chipset, resulted. Better than anything else it has, and certainly better than the IDE to CF adapter on my 4CoreDualSATA-SATA2, another experiment. (Boots MS-DOS 8.0 fine, Win98SE install pending).
The 4Core is already slated to use 2x IDE to 128GB SD adapters on the other IDE cable, and I thought I was done. Now, I may just pop in the X800XT AGP instead of the current Gainward 7950 PCIe, though, and see if I can't squeeze some crazy NVMe speeds out of one boot OS or another (98SE, XP, 7) using a PCIe4x adapter in the video card slot. (Another recent nicety on the 4Core is a floppy emulator that works like a charm.)
As you can see, I am trying to get all my legacy systems to transition to hybrid parts that I can still maintain well into the future.
If you want to go really retro, you get the HPIB to 2GB SD adapter that is coming in the mail for my trusty HP150 Touchscreen PC (DOS 3.0!), plus new caps for the damaged Tualatin PIII mobo that should house the HBIB to ISA card for directly attaching HP 150 drives to a PC.
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Why so nuts? Just retired, and the mothballs are flying out of the closets. Yippee. There's also a fairly pristine 4CoreDual-VSTA waiting for attention, which I just had to source, as that was my all-time run-away favorite, quirkly little board for many a year, as attested in this thread.