Short answer: choose the Radeon RX 7900 XTX when the workload needs more than 16GB and your tested ROCm stack supports it. Choose the GeForce RTX 4080 SUPER when the workload fits comfortably inside 16GB and CUDA compatibility is the stronger requirement. The Radeon’s extra 8GB can change whether a model stays on the GPU; the GeForce card’s software ecosystem can matter more when capacity is not the limit.
RX 7900 XTX versus RTX 4080 SUPER specifications
| Planning input | RX 7900 XTX reference | RTX 4080 SUPER Founders Edition |
|---|---|---|
| Architecture | AMD RDNA 3 | NVIDIA Ada Lovelace |
| Memory | 24GB GDDR6 | 16GB GDDR6X |
| Memory interface | 384-bit | 256-bit |
| Published processing units | 6,144 stream processors / 96 compute units | 10,240 CUDA cores |
| Boost clock | Up to 2.5GHz | 2.55GHz |
| Board power | 355W typical board power | 320W total graphics power |
| Recommended system power | 800W | 750W |
| Reference power input | 2 × 8-pin | 1 × 450W+ Gen 5 cable or supplied 3 × 8-pin adapter |
| Reference dimensions | 287mm, 2.5-slot | 304mm × 137mm, 3-slot |
| Primary software path | ROCm; verify exact OS, framework and operator support | CUDA, compute capability 8.9 |
Read the dedicated RX 7900 XTX 24GB guide and RTX 4080 SUPER 16GB guide. Broaden the shortlist with the 24GB buyer hub and 16GB buyer hub.
The 16GB versus 24GB boundary for a 32B model
| Official Qwen2.5-32B artifact | File size | 16GB raw margin | 24GB raw margin |
|---|---|---|---|
| Q2_K | 12.3GB | 3.7GB | 11.7GB |
| Q3_K_M | 15.9GB | 0.1GB — unsafe | 8.1GB |
| Q4_K_M | 19.9GB | Does not fit by file size | 4.1GB |
| Q5_K_M | 23.3GB | Does not fit | 0.7GB — unsafe |
| Q6_K | 26.9GB | Does not fit | Does not fit; 2.9GB over |
The 19.9GB Q4_K_M file is 3.9GB larger than the RTX 4080 SUPER’s advertised pool before overhead, while 24GB leaves 4.1GB before overhead. That establishes a capacity boundary, not a performance ranking. Use the 32B requirements guide and matched benchmark builder for your exact artifact, context and runtime.
ROCm versus CUDA can reverse the practical choice
The Radeon is useful only if the required application, operating system, framework and operators work on the chosen ROCm release. The RTX 4080 SUPER’s CUDA path may support more applications even when the Radeon has more memory. Verify unsupported operators, CPU fallback and offload before buying. Use the CUDA versus ROCm checklist.
Matched-test rules
- Hold model revision, artifact, quantization, context, cache, modality, prompt/output profile, batch, concurrency and timing boundary constant.
- Record exact board, OS, driver, backend/runtime, unsupported operators, fallback, CPU offload, exposed memory, peak memory, power limit and wall power.
- Do not compare a spilled or offloaded 16GB run with a resident 24GB run as though the memory path were identical.
- Do not assume two cards create one transparent pool; document partitioning and per-device peaks.
Once both paths pass the fit and software checks, compare current screened offers and seller condition rather than relying on launch pricing.