PCI Express Bandwidth Test: PCIe 4.0 vs. PCIe 3.0 Gaming Performance & Limited VRAM Memory Buffers - TechSpot

The folks over at TechPowerUp have tested an RTX 3080 with average frame rate performance at 1080p only dropping ~10% when limited to 4 GB/s of PCIe bandwidth.

AMD themselves would argue that the PCIe 3.0 bandwidth won’t be an issue for the 6500 XT as gamers should ensure they’re not exceeding the memory buffer for optimal performance, but with a 4GB graphics card in modern games that’s very difficult.

First, I tested both the 4GB and 8GB versions using their stock PCIe 4.0 x8 configuration, then repeated the test with PCIe 4.0 x4.

Given the 6500 XT and 5500 XT are expected to be fairly close in terms of performance based on benchmark numbers released by AMD, using the 5500 XT to simulate the potential PCIe issues of the 6500 XT should be fairly accurate.

Starting with F1 2021, we see that limiting the PCIe bandwidth with the 8GB 5500 XT has little to no impact on performance.

Then for the 4GB model we are seeing a 9% reduction in 1% low performance at a 6% hit to the average frame rate when comparing the stock PCIe 4.0 x8 configuration of the 5500 XT to PCIe 3.0 x4.

That’s not a massive performance hit, but it’s still a reasonable drop for a product that’s not all that powerful to begin with, though it does perform well in F1 2021 using the high quality preset.

although we're using the highest quality preset for this game, it was released back in 2018 and with sufficient PCI Express bandwidth, the 5500 XT can easily drive 60 fps on average, resulting in an enjoyable and very playable experience.

We see that PCIe bandwidth is far less of an issue for the 8GB model and that’s because the game does allocate up to 7 GB of VRAM using these quality settings at 1080p.

The 4GB 5500 XT plays just fine using its stock PCIe 4.0 x8 configuration, there were no crazy lag spikes, the game was very playable and enjoyable under these conditions.

Even when limited to PCIe 4.0 x4 bandwidth, we did see a 6% drop in performance, though overall the gameplay was similar to the x8 configuration.

When using PCI Express 4.0, the 4GB model was still able to deliver playable performance, while PCIe 3.0 crippled performance to the point where the game is simply not playable.

We're using the heavily dialed down ‘balanced’ quality preset, so those targeting 60 fps on average for these single player games will have some headroom to crank up the quality settings, though as we’ve seen you’ll run into performance related issues much sooner when using PCIe 3.0 with a x4 card.

PCI Express bandwidth aside, the 4GB buffer alone crippled the 5500 XT here, and reducing the bandwidth to x4 destroys performance to the point where the card can no longer be used.

But we see that limiting the PCIe bandwidth has a seriously negative impact on performance of the 4GB model.

Worse still, 1% lows are not below 60 fps and while this could be solved by reducing the quality settings, the game was perfectly playable even with 4GB of VRAM when using the PCIe 4.0 x8 mode.

This game is very demanding even using these settings, but with the full PCIe 4.0 x8 mode the 4GB 5500 XT was able to deliver playable performance with an average of 49 fps at 1080p.

The 1440p data isn’t that relevant as you can’t really play Cyberpunk 2077 with a 5500 XT at this resolution using the medium quality settings, but here’s the data anyway.

We tested Watch Dogs: Legion using the medium quality preset and although the 4GB model is slower than the 8GB version as the game requires 4.5 GB of memory in our test using the medium quality preset, performance was still decent when using the standard PCIe configuration with 66 fps on average.

We’ve heard reports that the upcoming 6500 XT is all over the place in terms of performance, and the limited 4GB buffer along with the gimped PCIe 4.0 x4 bandwidth is 100% the reason why and we can see an example of that here at 1080p with the 5500 XT.

Assassin's Creed Valhalla has been tested using the medium quality preset and we do see an 11% hit to performance for the 8GB model when using PCIe 3.0 x4, so that’s interesting as the game only required up to 4.2 GB in our test at 1080p.

The margins continued to grow at 1440p and now the PCIe 3.0 x4 configuration for the 4GB model was 32% slower than what we saw when using PCIe 4.0 x8.

Here we have a game that uses 7.2 GB of VRAM in our test at 1080p, using a dialed down medium quality preset.

But what’s really interesting is that the 4GB and 8GB versions of the 5500 XT delivered virtually the same level of performance when fed at least x8 bandwidth in the PCIe 4.0 mode, which is the default configuration for these models.

That means right away the upcoming 6500 XT is likely going to be heavily limited by PCIe memory bandwidth under these test conditions, even in a PCI Express 4.0 system.

Even so, reducing the PCIe bandwidth negatively impacted performance for both the 4GB and 8GB versions of the 5500 XT.

Interestingly, reducing PCIe bandwidth for the 8GB model still heavily reduced performance, dropping 1% lows by as much as 16%.

Here we’re comparing the average frame rate of the 4GB 5500 XT when using PCIe 4.0 x8, which is the default configuration for that model to PCIe 3.0 x4.

Beyond that we’re looking at double-digit gains with well over half the games seeing gains larger than 20%, and remember we’re using medium quality presets for the most part.

Now if we normalize the X axis and switch to the 8GB model, here’s how small the performance variation is there when comparing PCIe 4.0 x8 to PCIe 3.0 x4.

Titles such as Watch Dogs: Legion and Far Cry 6 were particularly intriguing, because despite exceeding the 4GB buffer, the 4GB version of the 5500 XT performed very close to the 8GB model when given the full PCIe 4.0 x8 bandwidth that those GPUs support.

However, limiting the 4GB model to even PCIe 4.0 x4 heavily reduced performance, suggesting that out of the box the 6500 XT could be in many instances limited primarily by the PCIe connection, which is pretty shocking

But this isn’t about the extreme cases, where we dropped to unplayable performance, it’s about the card being noticeably slower when using PCIe 3.0 x4 bandwidth

What’s more crazy is that when using the full PCIe 4.0 x8 bandwidth, the 4GB 5500 XT was 26% faster than the 4GB RX 570, but when limited to PCIe 3.0 x4 it ended up slower than the old RX 570 by a 12% margin

So we'll say that again, the 5500 XT was 12% slower than the RX 570 when both are using PCI Express 3.0, but the 5500 XT was limited to 4 lanes whereas the 570 used all 16