> at the rate AI is currently progressing, i think you'd be optimistic to consider that as having a 2 year depreciation.

How so? Model capability at a fixed hardware level has been consistently (and rapidly) increasing. You might or might not be able to run state of the art 2 (or 4 or whatever) years from now but you can reasonably expect the hardware to last upwards of a decade with model performance consistently improving over that time frame.

You can get a tolerable (at least by some metrics) experience using 10 year old hardware today.