So you basically can't buy a computer today with 1 core, nor would you want to. That guidance is to say "don't go out and buy a 32 core Threadripper at 3ghz" and expect performance to be better than a quad core at 4.5ghz, for the task of running most operations in most CAD software.
As far as most operations in most CAD software are concerned, without getting into details, they are performed on a single thread, meaning on one core. So if you have your 32 core threadripper, that operation will occur at 3 ghz on one core. On your quad core 4.5ghz computer, it will occur at 4.5 ghz, faster. Now if you're running Keyshot, the Threadripper will blow the quad core out of the water. So it depends.
It doesn't have to be super complex - find the highest clockspeed quad core, which likely has 4 physical and 4 virtual cores for a total of 8, that you can afford.
Keep in mind that your choice of processor also affects other things, most notably the motherboard since different processor generations and manufacturers use different sockets. So, if you are actually specifying a 'computer' versus 'a processor' that you might plug into an existing computer, the suggestion perhaps becomes a bit different.
So, let us know if you want a processor or a computer suggestion, and what the budget is.
