1989: Odd that the superminicomputer that cost hundreds of thousands had 8MB RAM and managed 1 MIPS, while my Acorn Archimedes cost $2000 had 1MB (and you could get up to 4MB) and managed 8 MIPS.
The paper was written in 1988 and published in 1989 (1 Jan 1989, so just). The Prime 750 is specifically named in the paper, it was probably the best system he had access to when doing the work.