AMD Radeon RX 6600 XT with 8 lanes on PCIe 3.0 and without Resizeable BAR – Dream or nightmare for upgraders?

1 - Introduction and Test System 2 - Gaming Performance Full-HD 3 - Gaming Performance WQHD 4 - Gaming Performance with and without FSR 5 - Details: Frames per Second (Curve) 6 - Details: Percentiles (Curve) 7 - Details: Frame Times (Bar) 8 - Details: Frame Times (Curves) 9 - Details: Variances (Bar) 10 - Power Consumption and Efficiency 11 - Overview, Averages and Conclusion

The recently launched AMD Radeon RX 6600 XT has a small disadvantage based on the parallel use in notebooks: there are electrically only a total of 8 lanes connected to the PCIe 4.0. Of course, this is nominally enough for such a FULL HD card, which you can also still use quite well in WQHD. But what happens if you only have an older system with PCIe Gen. 3.0? After all, the bandwidth of an older generation connection halved from 16 to 8 lanes certainly costs performance. This was also the case with the much weaker Radeon RX 5500 XT and that’s exactly what we want to find out today.

So dream or nightmare for upgraders with older systems? The RX 6600 XT are quite interesting, because these cards were available as a custom model for a short time at an MSRP of just under 380 Euro, which was still a lot, but still relatively little in relation to the larger cards. Stupidly only that the trade drives up the prices meanwhile already again hand-teasingly up to scarcely 500 euros, although the manufacturers supply to fixed prices. So it’s not up to AMD or the board partners, it’s up to the greedy chain all the way to retail in Germany. There is nothing I can do, except benchmarking and hoping that this madness will finally come to an end and the scalpers will be left with their hoarded devotional objects at the highest possible loss.

Foreword to the review of the Radeon RX 6600 XT with PCIe 3.0

As we know, the AMD Radeon RX 6600 XT relies on the Navi 23 XT GPU, which has 32 compute units or 2048 stream processors. The card also features 32MB of Infinity Cache and 8GB of 16Gbps GDDR6 memory running over a 128-bit wide bus interface, which then gives a total bandwidth of 256GB/s.  And it is precisely this that must be able to be used. However, the Radeon RX 6600 XT is only electrically connected to 8 lanes and that’s of course where the questions start.

I have received a lot of feedback from readers of the website and viewers on YouTube. Most of them still use much older systems, which rely on PCIe 3.0 and are often not even suitable for Resizeable BAR (SAM) after a BIOS update. I have noticed in first plausibility tests that SAM can definitely eliminate smaller deficits, but in the end it can’t help to compensate the existing performance loss due to the bottleneck of the 8 lanes at the PCIe 3.0.

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Since my benchmark selection includes titles with and without SAM support anyway, to eliminate the inaccuracies I changed both the PCIe slot to Generation 3.0 and the chipset to be as close as possible to the older systems, at least in this regard. In addition, I have disabled SAM in general. SAM could, assuming a really fast “old” CPU and fast memory, of course still save a percentage point or two in the best game and Full HD, but this stroke of luck occurs so rarely that you can actually leave it out. After all, who runs an Intel Core i7-8700K or 9900K overclocked to 5 GHz with such a card?

Benchmarks, Test system and evaluation software

For the benchmarks, analogous to the launch article of the Radeon RX 6600 XT , I chose the same games and settings, where two games directly handle both DLSS and FSR. The benchmark system was completely changed to PCIe 3.0. This includes the matching X570 motherboard in the form of the MSI MEG X570 Godlike and a select Ryzen 9 5900X that has been water-cooled overclocked (PBO + 500 MHz). Add to that the matching DDR4 4000 RAM from Corsair, as well as several fast NVMe SSDs. For direct logging during all games and applications, I use my own measurement station with shunts and riser card, as well as NVIDIA’s PCAT in games, which adds to the convenience immensely.

The measurement of the detailed power consumption and other, more profound things takes place here in the special laboratory on a redundant and in detail identical test system then double-tracked by means of high-resolution oscillograph technology…

…and the self-created MCU-based measurement setup for motherboards and graphics cards (pictures below), where at the end in the air-conditioned room also the thermographic infrared images are created with a high-resolution industrial camera. The audio measurements are done outside in my Chamber (room within a room).

I have also summarized the individual components of the test system in a table: