"80-wire cables" issue when using SATA drives in PATA Thinkpads

I'm trying to use a SATA M.2 drive in a Thinkpad X30 and am bumping into
a ~30MB/s bandwidth limit that's apprarently imposed by the "lack" of an
80-wire cable (which of course can't exist on 2½ drives).

This is mentioned at the end of https://www.thinkwiki.org/wiki/How_to_put_SATA_in_old_ThinkPads
and links to
https://forum.thinkpads.com//viewtopic.php?f=31&t=115478&p=741729

which mentions this as a known problem.
Is there some known workaround for it?

I tried to boot with `libata.force=80c` and it does result in `hdparm`
showing me that `udma5` is used instead of `udma2`, but that seems to be
a lie because the actual bandwidth I see is still ~30MB/s.

30MB/s is actually still usable (it makes the drive about as fast as my
previous PATA drive in terms of bandwidth while still benefiting from
the much lower latency), but 60MB/s or even 120MB/s would be most
welcome nevertheless.


        Stefan

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