Should I keep my Arc B580 or look for another GPU?

I'd keep the B580 unless you find a specific alternative that fits your budget and power supply. A new card gives you a warranty, and the 12GB of VRAM is worth considering if you want to avoid turning down texture settings in demanding games.

Before deciding, check benchmarks for the games you actually play, ideally with a similar CPU. Also check that your motherboard supports Resizable BAR and that it's enabled, since Arc cards can lose performance without it.

A new RTX 5060 is another option around that price if you can find one. You'd get access to DLSS and frame generation, but it has 8GB of VRAM rather than the B580's 12GB. Whether that's a worthwhile trade depends on your games and settings. Don't assume either the extra memory or the features make one card automatically better for you.

Used can get you more performance for the money. An RTX 3080 around $300 would be tempting, and a used RX 7700 XT or 7800 XT would also be worth checking if one turns up within budget. Those prices aren't guaranteed, though.

The 3080 draws a lot more power, so check the exact card's power requirements and your power supply's quality and connectors before buying. A power limit can reduce draw, but it doesn't guarantee that a particular 650W unit will be suitable.

Don't compare a used listing with a new card on price alone. Check the seller's return policy, whether the card can be tested, and what condition it's in. A bargain is less appealing if you have to troubleshoot it or replace thermal paste and pads soon afterward.