Looks like the IO area may need modification if you want to swap the motherboard. Looks like it could be a good deal depending on what you can negotiate.
There’s a few different configs available.
$279 + shipping, OBO
$299 + shipping, OBO
$240 shipped for a CSE-847 variant almost sounds like a good deal.
If not for the following problem - X400 is officially specced for SATA 2.0 only. I am not sure where the limitation comes from. SATA3.0 was finalized in 2009 and X400 has been released in 2012.
Hardware-wise x8dt6-a-is018 is just a regular X8DT6 with onboard SAS2008 - so HBA is not the limiting factor. I am afraid that the SATA2.0 restriction might be caused by the backplanes. Since this is not a standard CSE-847 - there is no information available from Supermicro. But there is slim chance that it only needs a SAS expander firmware update to support SATA3.
So unless someone who has the unit can confirm that it is SATA3/SAS2 capable - I would pass.
SATA 2 can do theoretical 300MB/s, in reality around 250MB/s.
Why is that an issue for hard drives?