I'd go for the latest chip with 16GB and the way you use your. computers it will last you for years. Cashvill2 2400 got a great deal on an open box. There is all sorts of good and useful discussion and argument here, but the lines that makes me laugh are the one that says XYZ is "definitely" coming out in ______ (fill in the blank). If anything were ever definite with Apple there would be many fewer people addicted to MacRumors and other future oriented Apple websites. Usually we don't know anything definite until a few weeks, days, sometimes hours before. And that's when there isn't a pandemic wreaking havoc on the world's supply chains. Forget definite. Buy what you need now, enjoy it tomorrow and the next day, and let the future comes when it does and how it does.
While the spirit of what you're saying is true you're acting like Apple didn't announce in June that they are releasing ARM Macs this year. It's not even a rumour, it's straight from the horses mouth. It's also pretty obvious that the computers with 2 year old processors are the most likely to be updated. There's no sense in being wilfully ignorant just for the sake of it.