Linux for Leftists

For RAM, it's better to go 2x8GB than 1x16GB due to the way the CPU interfaces with the memory. You can get just one stick and the system will work, but having two for dual-channel mode improves performance.

Cores and clock speeds and boost clocks are...complicated, and most of the numbers are only useful with comparison between other products in the same line and sometimes competing products in the game generation. A 4GHz processor from five years ago will probably be slower in almost every task than a 3GHz processor from today due to improvements in instructions-per-cycle and other things.

The way I would go about this: first, figure out what your budget is. Find a current-generation processor within that budget and find some benchmark data for it. Then, start looking at previous-gen or even older, used processors at the same price point and find benchmark data from them to compare. In terms of performance-per-watt, newer is almost always better, but performance-per-dollar takes a bit more digging. Also worth considering, while the motherboard itself will have a negligible impact on performance in most cases, the prices of older (and, again, especially used) motherboards can be substantially cheaper so you might be able to save even more money by going previous-gen than the difference in CPU prices alone. To a point though, beyond a certain age, motherboards/RAM are hard enough to come by that they tend to increase in price again.