Benchmarks Show RTX 4090, 4070 Ti Take A Big Performance Hit With External GPU Boxes

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The typical image of the mighty NVIDIA GeForce RTX 4090 inside a glorious PC build is something a set any enthusiast's heart aflutter. Seeing this same powerhouse GPU connected to a mobile device outside of its usual habitat can also be an equally interesting sight. However, when enthusiasts learn of the potential 20% drop in performance, that enthusiasm may wane a bit.

A user on Weibo recently demonstrated this use case with a GeForce RTX 4070 Ti Super and a GeForce RTX 4090 connected externally via OCuLink. OCuLink is an external PCIe connection; while Thunderbolt 4 tops out at a paltry 40 Gbps, OCuLink's PCIe 4.0 x4 connection offers ~63 Gbps. This increase is notable, but there are significant drawbacks to be aware of. According to these performance results, users can still expect a significant drop in performance for GPUs connected in this manner. 

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GeForce RTX 4090 scores much lower via OCuLink with Time Spy 

Whilst connected to a traditional motherboard and high-end CPU, the GeForce RTX 4090 typically will achieve a Time Spy graphics score of over 36,000. Via OCuLink on an external device, the score drops in the range of 20% to a low of 28,230 as tested. It's worth mentioning that this low score was achieved when connected to the laptop's internal screen. When an external display was used instead, the score went up to 30,429—better, but still well under the usual desktop score.

The NVIDIA GeForce RTX 4090 is notorious for needing the fastest CPU possible, especially at lower resolutions. When gaming, for example, a less-capable CPU will bottleneck this GPU at any resolution below 4K, and even at 4K in some games. The test machine's Core Ultra 5 125H is certainly pretty fast, but a 28W mobile part doesn't hold a candle to something like a Core i9-14900K. With that said, given that we're comparing Graphics scores here, that's less of a factor.

GeForce RTX 4070 Ti Super with a near 10% loss via OCuLink

The comparatively less-powerful GeForce RTX 4070 Ti Super seems to have less of an overall performance loss when connected in the same manner as the GeForce RTX 4090, staying in the neighborhood of 10%. On a desktop, the GeForce RTX 4070 Ti Super will be less susceptible to CPU bottlenecks, but it can still suffer a CPU limitation at lower resolutions, or when paired with a weaker CPU. 

When the GeForce RTX 4090 was tested using Time Spy Extreme, which runs at 4K resolution, the bottleneck appeared to be significantly less than the standard 1440p Time Spy test. Once again, the CPU is less important at higher resolutions, where the bottleneck typically moves over to the GPU. This will free up the GeForce RTX 4090 to flex more of its brute-force muscle, even when connected via OCuLink. 

Even with this drop in performance, these OCuLink connected GPUs can still be an attractive option for users who frequently use a docking station but absolutely need to be mobile. When connected to a less graphically-capable device, such as a laptop, they can still offer a much higher level of graphics performance.  The reduced PCIe bandwidth also has a smaller effect on compute and AI workloads that can reside directly on the GPU.