The RX 7900 XT 20GB has about 59% more memory bandwidth (800 vs 504 GB/s). Batch-1 decode tracks bandwidth closely, so a model that fits both cards should decode roughly 59% faster on the RX 7900 XT 20GB. The RX 7900 XT 20GB fits more of the catalog at Q4/8K — 32 vs 18 of 61 models (20 vs 12 GB VRAM). Largest model that fits the RX 7900 XT 20GB but not the RTX 4070 12GB: GLM-4.7-Flash (31.2B). MSRP is $599 for the RTX 4070 12GB vs $899 for the RX 7900 XT 20GB. 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 XT 20GB posts the higher tok/s in 32 rows vs 8. Methodology.