So... after 2.5 years of owning a Thinkpad T400, first librebooting, then gradually modifying the shit out of it, I have to say that an Intel Core 2 Duo CPU is still completely sufficient for everything I'm doing today.
Everything packaged for Debian still runs perfectly smooth. And yes, this includes all the games.
I'm saying this because I want to make a stand against planned obsolescence and new hardware craze. Your old machine is very likely still fine. Please use it a little bit longer 🙂