The L40S 48GB has about 89% more memory bandwidth (864 vs 456 GB/s). Batch-1 decode tracks bandwidth closely, so a model that fits both cards should decode roughly 89% faster on the L40S 48GB. The L40S 48GB fits more of the catalog at Q4/8K — 39 vs 18 of 61 models (48 vs 12 GB VRAM). Largest model that fits the L40S 48GB but not the Arc B580 12GB: Qwen3-Coder-Next (79.7B). MSRP is $249 for the Arc B580 12GB vs $8,000 for the L40S 48GB. 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 L40S 48GB posts the higher tok/s in 33 rows vs 7. Methodology.