Even without optimizations. That page is from 1997. They probably ran this on a 200MHz machine at best. Modern CPUs are 30-50x faster just in terms of instructions per second. Then once you factor in multiple cores, we have desktop machines that are easily 100x faster.

In terms of optimizations we have SIMD and GPGPUs to make it even faster. Not unrealistic to think we could bring that 6 minute figure down to one second... And then, of course, there might be algorithmic tweaks that help us even more. Get 100 people looking at that code, and for sure they'd find ways to speed it up.

Modern images are also much much higher res compared to "320x200 true-color image".

Without knowing how this scales with image size there is really no way to speculate about performance on modern hardware.

In the same magazine there is an ad for a $3795 Gateway 2000 workstation. 486DX2 66MHz, 8MB RAM, 500MB SCSI HDD, SVGA graphics with 1MB RAM, 14" CRT.

I remember looking at systems like that and drooling. Now the latest CPUs have 8MB L3 cache.

Theres 8-core i7s with 20MB L3 cache now.