VAX were relatively small computers for the time. They grew upward in the late 80s eventually rivalling the mainframes for speed (and cost). But in the early 80s IBM's high end machines were an entire order of magnitude larger.

Top of the line VAX in 1984 was the 8600 with a 12.5 MHz internal clock, doing about 2 million instructions per second.

IBM 3084 from 1984 - quad SMP (four processors) at 38 MHz internal clock, about 7 million instructions per second, per processor.

Though the VAX was about $50K and the mainframe about $3 million.