The supercomputers of the time were very heavily designed to run floating-point operations (IIRC) and so while the FPU performance might be comparable, I'm not sure a Cray could be used as a "1/4 speed Pi" for general computing things like running Linux.
I used a Cray around 1998 (from the Pittsburgh Supercomputing Center IIRC) and it was super fast on very particular tasks. Specifically, there was some type of processing pipeline that once you had it set up, it would produce a stream of calculations very quickly.
I wonder if the Raspberry Pi is faster on all tasks, or is there some type of computation the old Cray is still competitive?
I suspect the Cray is "competitive" for some value of "doesn't absolutely stink" for things that are designed for it.
But you can emulate a Cray on an FPGA: https://www.chrisfenton.com/homebrew-cray-1a/ so I suspect that while it could still do "real work" you can also beat the pants off it if you setup your code as designed to run on modern GPUs.
