The RX 7900 XTX 24GB has about 111% more memory bandwidth (960 vs 456 GB/s). Batch-1 decode tracks bandwidth closely, so a model that fits both cards should decode roughly 111% faster on the RX 7900 XTX 24GB. The RX 7900 XTX 24GB fits more of the catalog at Q4/8K — 33 vs 18 of 61 models (24 vs 12 GB VRAM). Largest model that fits the RX 7900 XTX 24GB but not the Arc B580 12GB: GLM-4.7-Flash (31.2B). MSRP is $249 for the Arc B580 12GB vs $999 for the RX 7900 XTX 24GB. MSRP is a launch list price, not live retail — Amazon prices move; click through for the current price. In the Q4/8K head-to-head below (40 shared models), the RX 7900 XTX 24GB posts the higher tok/s in 34 rows vs 6. Methodology.