If you ran exactly the same code on a modern machine I'd say that's a pretty reasonable guess.

You'd get a big speedup just by going from single-threaded to multi-threaded execution. Probably the biggest boost would be to use modern methods. It's possible to do path tracing at interactive frame-rates on modern hardware; some of the optimizations can include not doing very many samples per pixel but to rely on denoising algorithms that can take advantage of the redundancy inherent in the image to smooth out the graininess of course global illumination effects. There are a lot of other algorithmic improvements too; modern acceleration structures, techniques to preferentially sample rays that are most likely to impact the final result, etc..

POV-Ray is amazing software, but it wasn't really ever meant to be an interactive renderer. It kind of leans towards maximum extensibility over raw performance. Modern renderers are usually much faster.

I doubt you'll get any speedup from multi-threaded execution, unless it is also multi-core.

It’s hard to find processors these days that aren’t multi-core. I can’t remember the last time I saw a single-core computer.

(Or are you talking about the difference between “multi-threaded execution” and “multi-core execution”? That wouldn’t make sense. Threads are how you execute code on multiple cores.)

That's what I meant; multiple operating systems threads, not hyperthreaded execution on one core.

I don't remember offhand what POV-Ray's support for multi-core execution is or was. Back in the 90's, there was PVM-POV which ran on a cluster. That's probably what you'd use if you had a dual-socket machine back then. I imagine there was probably an MPI version as well. I assume it supports multicore natively now, since practically all CPUs are multi-core now.

Less than that even, since in the old days there was likely lots of swapping. A machine of that vintage was likely only on 4mb of RAM. Just the frame buffer would eat up about half of that

Pentiums weren’t that old. It would depend a lot on gpu rather than cpu.

POVray doesn’t use gpu. It is embarrassingly parallel though. I would expect say a 2000x speedup over a Penguin 1 though. Say, 40x the raw clock x 2-3x more per cycle x 12-16 cores

Those 1st generation Penguins were slow, not even a flight coprocessor