I think an X230 would be performant enough for 95% of the things I do, but a 14 year old CPU is going to have pretty terrible battery life for anything more than very light usage. And things that would be light usage on a recent PC, like watching video encoded with a modern codec, would be fairly taxing on an old CPU with no hardware decode.

True. By the time I upgraded from my X200 (fantastic machine, noticeably outdated), the lack of software support for hardware decoding H264 was noticeable. Also being stuck with OpenGL 2.1 isn't the best either.

I don't know what I'll do if and when my X230 stops being sufficient. If I could buy an Apple motherboard in an X200 chassis I'd do it in a heartbeat.