I recently found myself in the unusual situation of having a fairly large budget to buy a new laptop for work, and running Stan models was one of my main drivers for choosing the system specifications. (It’s typically the most demanding thing my laptop has to handle.)
To answer the question for people who aren’t looking to buy a MacBook, I followed the advice here and eventually ordered a Thinkpad P1 Gen2 with the Intel Core i9-9880H Processor and 64GB RAM (and an NVIDIA Quadro T2000 GPU). There are faster machines out there, such as the Thinkpad P53 and workstations from other manufacturers, but the P1 has the advantage of still being a fairly slim and portable 15".
At the top end of the CPU specifications, the P1 has an option of an Intel Core i9-9880H Processor or an Intel Xeon E-2276M. The i9 has eight cores, with 512K L1 cache, 2MB L2 cache, and 16MB L3 cache. The Xeon is six cores with 384 KB L1 cache, 1.5 MB L2 cache, and 12 MB L3 cache. The Xeon’s main advantage is support for ECC RAM at the cost of slower performance, so the i9 seemed much the best option.
To be honest, though, I get the impression that “lots of RAM, as fast as possible, lots of cores, lots of cache” is probably enough for most people when making the decision, and much more comes down to building models well. For anything truly taxing, I would be looking to offload the model to my department’s compute server. It is nice to be able to iterate reduced versions of models locally before doing that, though.
(And, for reference, that’s advice very much from a Stan novice who hasn’t yet had their shiny new laptop delivered after 8 weeks of waiting…)
EDIT: All this is in the context of (Arch) Linux, although with 4TB of drive space I’ll likely be dual booting with Windows 10.