I'd be interested to know if the SATA interface is being saturated (or near saturated) even when say an 850 PRO is transferring a tonne of tiny files (e.g. overheads to do with instructions), or whether it might be possible to push 500MB/sec over SATA 6Gbps for even the smallest of files. Considering the best stat I've seen for a SATA SSD when transferring the tiniest amounts of data is about 50MB/sec (testing with ATTO), that would probably be a performance difference worth paying for in the realm of SATA SSDs.