The subjectively fastest, which is to say the most responsive or lowest input latency, computer I've ever used was a Macintosh 512ke upgraded to 2.5 megabytes of memory, running the system software and apps off of a 1.5 megabyte RAM-disk. When you double-clicked, say, MacPaint in the Finder, it was loaded before you finished the physical mouseup. This was when that hardware and software was still current.