Hi and welcome to TFP!
Note: In your research, beware of the marketing tactics on the product you are looking at. You will read that many of the VS pumps, for example, offer the ability to program 8 speeds. That is partially misleading. That flexibility exists only with an external controller, such as an Intellitouch (for pentair pumps). If programming speeds from the pump controller, you only have 3 or 4, depending on the model. SO, in order to know what is what, read the whole owner manual so that you dont end up with a product that doesnt fit your expectations.
I was curious about this; also considering a VS pump to replace a 3/4hp single speed from 2005 -- are the 4 or 8 speeds the number of different settings you can have (e.g 1 hour at speed A, 2 at speed B, etc), with each selectable across a much more granular RPM range? Or is it that there are only 8 (or 4) steps from slowest to fastest? If the latter, would that mean that if I'm replacing 3/4hp fixed with 3HP variable, that there really are only ~2 speeds that are equivalent/lower than the existing pump (thus making it not much better than a 2-speed)?