Radeon RX 7900 XTX and GeForce RTX 4090 each provide 24GB of dedicated memory. That gives the same model file the same nominal file-only margin, but it does not make the cards interchangeable for local AI.
Capacity is a tie
In the official Qwen2.5-32B-Instruct-GGUF repository, Q3_K_M is 15.9GB and leaves 8.1GB before cache and runtime allocations on either card. Q4_K_M is 19.9GB and leaves 4.1GB. Q5_K_M is 23.3GB and leaves an unsafe 0.7GB. Q6_K at 26.9GB and Q8_0 at 34.8GB fit neither card wholly.
Software is not a tie
RTX 4090 uses NVIDIA’s CUDA ecosystem. RX 7900 XTX requires a verified AMD path such as the exact supported ROCm release, OS, driver, framework, runtime, backend, kernels and operators. CUDA-only software does not become compatible because memory capacity matches. Windows, WSL and Linux support claims must be checked separately.
Power and measured behavior decide the rest
NVIDIA lists 450W total graphics power and 850W required system power for the RTX 4090 reference design; AMD lists 355W typical board power and an 800W minimum PSU recommendation for RX 7900 XTX. Those figures are planning inputs, not workload efficiency results. Hold artifact, quantization, context, cache, backend, runtime, prompt/output profile, concurrency and timing constant; record fallback, offload, peak device memory and complete-system wall power.
Published October 25, 2026. HighVRAM has not independently benchmarked this pair. Official specifications and file-size arithmetic do not establish application speed, output quality or value.