Does PCIe 3.0 x16 perform better than PCIe 3.0 x8 for a modern GPU?

For ordinary gaming, PCIe 3.0 x16 is generally fine, and even PCIe 3.0 x8 may be acceptable depending on the GPU and game. Testing tends to show small differences when VRAM usage stays within the card's capacity, often around a few percent or within the margin of error. The gap can become much larger in demanding scenes with an 8 GB card that is already VRAM-limited.

I would personally choose an x16 GPU if the price and performance are otherwise similar, particularly for a PCIe 3.0 system. Aim for at least 12 GB of VRAM if possible. An x8 card is not automatically a bad purchase, but it leaves less bandwidth available and gives you less headroom for future, more demanding games.

PCIe bandwidth roughly doubles with each generation: PCIe 3.0 x16 is equivalent to PCIe 4.0 x8 or PCIe 5.0 x4. In most current games, the difference between PCIe 3.0 x16 and x8 is small, especially when the card has enough VRAM. However, an x16 card is the safer choice on a PCIe 3.0 system, since x8 cards have only half the available bandwidth and can suffer more when data has to spill beyond VRAM.

The important distinction is whether the card is natively wired for x8 or whether the motherboard is limiting an x16 card. A modern x8 card on PCIe 3.0 has bandwidth similar to PCIe 2.0 x16, while an x16 card gets the full PCIe 3.0 x16 bandwidth. Usually the performance loss is minor, but it becomes much more noticeable if the GPU runs out of VRAM and has to move textures and other data across the PCIe bus.