The benchmark function has been modified with the different Matlab versions, such that you cannot compare the results between a Matlab 6.5 machine with R2019a. You need to decide for a specific benchmark version at first. I do not know, if delays in the audio interface are considered at all in the benchmark tools.
What is "the average PC available to students in 2000"? If it was a single core, the activity of the virus scanner is essential for real-time processing. The "average" PC in 2000 might use 1.6 cores - but this is not meaningful.
The graphics output has slowed down dramatically in the last years, especially with introducing HG2. While creating or updating a simple GUI with some buttons takes seconds today, it ran in 0.4 seconds in R2009a and 0.2 seconds in R6.5. (Note: I took these timings on a 4-core i7 for Matlab 2018b and 2009a, but on a PentiumIII for R6.5.) But if you draw 3D patch objects with hundreds or thousands of elements, modern Matlab versions will outperform the older ones.
This means that asking for benchmarks will not be only "imprecise", but not useful in any way to estimate the performance of a very specific job. It is like asking for the average speed of cars in the last 100 years: It depends on the roads and the speed limits, on the relation between high-ways and streets inside cities, and on the decision if trucks are considered as cars or not.
