Sorry for what may be a stoopid question.....but-

Can an Intel 660p Series M.2 2280 1TB PCIe NVMe 3.0 x4 3D2, QLC Internal Solid State Drive (SSD) be used as a cache drive? 

Yes, but note that write performance will suffer since it's QLC.

Thank you for the response.

Would the speed make that much of a difference in a cache drive? Wikipedia shows it as the slowest choice, but doesn't show a speed comparison.

IIRC sustained write speed once the small SLC cache is full drops to 100MB/s, so slower than a fast HDD, if that's acceptable or not depends mostly on your use case, reads are still fast.

Edited July 2, 20197 yr by johnnie.black

Thank you so much, that helps a lot. 

Think I'll just use a good HDD.

9 minutes ago, lockrob2000 said:

Think I'll just use a good HDD.

That's good if cache will be mostly used for data transfer, if you're going to run VMs any SSD is much faster mostly because of the random access performance difference.