Comment by adrian_b

A 5-year old card, i.e. an NVIDIA Ampere RTX 30xx from 2020, is perfectly fine.

Even 7-year old cards, i.e. NVIDIA Turing RTX 20xx from 2018, are still acceptable.

Older GPUs than Turing should be avoided, because they lack many capabilities of the newer cards, e.g. "tensor cores", and their support in the newer CUDA toolkits will be deprecated in a not very distant future, but very slowly, so for now you can still create programs for Maxwell GPUs from 10 years ago.

Among the newer GPUs, the RTX 40xx SUPER series (i.e. the SUPER variants, not the original RTX 40xx series) has the best energy efficiency. The newest RTX 50xx GPUs have worse energy efficiency than RTX 40xx SUPER, so they achieve a somewhat higher performance only by consuming a disproportionately greater power. Instead of that, it is better to use multiple RTX 40xx SUPER.