If those drives were short-stroked, they probably could have kept up with that SSD, though at a reduced capacity. SSD would probably have a lower power bill over its life, though. I did some calculations for an array of short-stroked 15k SAS disks to replace a consumer 4GB SSD for a write-intensive app that chews through SSDs, and its performance would be in spitting distance of the SSD. Ended up not doing it due to likely not having any parts availability for 15k SAS drives in the not too distant future.
Except that we would have needed a lot more than the 8 drives then, to keep the same capacity. I think it was 1TB of storage around 1999. For mail storage it unfortunately needed both capacity and seek latency.
