Dont' be fooled by the Costco version.
Yes it was on sale last week for -$200 less than retail. But the problem with that is, Costco's version is hugely specced down.
Instead of giving consumers the MVNe PCIe SSD on the 512gb storage, they included older technology, which is SATA3. Many might not know the difference between the two, but basically it largely translate to 3x the read and write speed. I bought the version and tested it myself. SATA3 reads at around 550Mb/s and writes at around 350Mb/s. For MVNe PCIe drives, your suppose to see 1500Mb/s reads and 1100Mb/s writes. The difference can largely been see when your transfering large files. May also reflect when your booting the computer as well. So yes, you pick if you want old tech and spend less, or get the real deal.
BTW, keep in mind that the SP4 does come with MVNe PCIe ssd.