First of all a little disclaimer. I’m no expert for this either. This is just what I personally think would be best but I have no particular experience.
Generally weak gear or even middle wear gear is not ideal for development. You shouldn’t make compromises to have more variety there.
However I would suggest to have at least one AMD and one Intel / Nvidia rig with equal power (with that I mean equal stats on paper. For example an I7 4k something with 3.4 GHz and a similar quadcore from AMD so you have a direct reference between those).
This will show you how large the difference between those two structures is and you can give reliable estimates for both systems.
Again I am not talking from experience (in game development) but for other software and generally for games there is most of the time a difference between those systems with equal specs.