I've been replacing a lot of my older cards because I get tired of the office being an oven. It still is, but not as bad lol. Newer Nvidia cards are really the only way to go. AMD just isn't very competitive for F@H.
I replaced my 6950XT with a 5070Ti and it's been great. Little over quadruple the PPD while sipping less power.
Really anything RTX 40 or 50 series is great for folding. All the 8GB cards are pretty equally hated by gamers so they can be found relatively cheap when people upgrade their prebuilt rigs. So, 4060 or 5060 and the TI versions of those cards. They also undervolt pretty well to further drop the power consumption without losing hardly any PPD.
4070 and 5070 are in a weird spot. They typically go for more than I'd like to spend on a secondary card that's mostly for folding. Being a 12GB card, they are not something I'd put in any of my main rigs. IF you find one for a great deal, they are solid cards.
4070 Ti is in the same boat as the above. The 4070 Ti Super and 5070 Ti are 16GB cards and good candidates for a main GPU and also really strong for F@H.
4080 and 5080 are again in a bit of a weird spot where the jump in cost outpaces the jump in performance from the previous tier.
4090 and 5090 are god tier for PPD, but are way overpriced. Thanks AI...