AMD introduced PCIe 4.0 with the Ryzen 3000 series CPUs and Navi-based RX 5700 series GPUs. The new standard doubles the throughput over last gen. Testing, however, showed that there was very little difference between PCIe 3.0 and 4.0 graphics performance on the x16-capable RX 5700 XT. The recently launched budget-oriented RX 5500 XT, though, is limited to 8 lanes only, and as PCGH has found, it may be crippling the performance of the card on a PCIe 3.0 platform possibly due to saturation of the available bandwidth.
Currently, only AMD's flagship X570 chipset supports PCIe 4.0 in the mainstream segment, and it was pitted against Intel's Core i9-9900K platform, which is still on older PCIe 3.0. An AIDA64 GPGPU graphics benchmark test using the RX 5500 XT showed the Ryzen system outperforming the Intel one by about two times in the GPU memory reads and writes.
|Ryzen 5 3600 / X570 chipset
|Intel Core i9-9900K
|Memory Read||13331 MB/s||6755 MB/s|
|Memory Write||13211 MB/s||6586 MB/s|
A few VRAM-heavy games were also tested to measure the effect of the fewer PCIe lanes on both 4GB and 8GB flavors using AMD's Adrenalin 2020 edition driver.
From the tests, it appears that the 4GB variant, especially on the PCIe 3.0 platform, has struggled the most. The slower memory read and write speeds - as seen from the AIDA64 numbers - seem to be further hindering the performance of the 4 gig card. If the finding here is accurate, then the 4GB RX 5500 XT will consequently become very difficult to recommend as the majority of the people shopping with this budget will likely not opt for expensive PCIe 4.0-capable X570 motherboard offerings.
There's also a possibility of some other issue being at play here, which will require further investigation to confirm.