NVIDIA RTX 4080 vs NVIDIA RTX 3080 10GB

Analysis

The RTX 3080 and RTX 4080 are separated by two years, one architecture generation, and $500 in launch price ($699 vs $1,199), but VRAM capacity, not raw speed, is what actually separates them for local LLM work. The RTX 3080's wider memory bus gives it slightly more raw bandwidth than the newer, pricier card, a genuine surprise this site's calculator confirms directly.

NVIDIA's Ampere-generation RTX 3080 pairs 10GB of GDDR6X with a 320-bit bus for 760 GB/s; the RTX 4080's Ada Lovelace AD103 die runs a narrower 256-bit bus at 717 GB/s, 6.0% less bandwidth despite two years of architecture progress and 60% more VRAM (16GB vs 10GB). Since decode speed is bandwidth-bound, that gap shows up directly for any model both cards fit: Llama 3.1 8B at its recommended Q5_K_M decodes at 83.0 tok/s on the RTX 3080 versus 79.1 tok/s on the RTX 4080, and Qwen 2.5 7B at Q4_K_M reaches 107.5 tok/s versus 102.5 tok/s, both a real edge of roughly 5% for the older, cheaper card, just under its 6% bandwidth advantage. What the RTX 3080 can't do is hold larger models at all: Qwen3 14B at its recommended Q5_K_M needs 13.31 GB, comfortably inside the RTX 4080's usable VRAM (47.1 tok/s) but past the RTX 3080's 10GB ceiling, dropping to a CPU-offloaded 8.9 tok/s. GPT-OSS 20B, a model OpenAI explicitly sized to fit a 16GB card, shows the same pattern: 173.4 tok/s native on the RTX 4080 versus 43.8 tok/s offloaded on the RTX 3080 (a mixture-of-experts model streams only its active experts from system RAM, so it degrades far more gracefully than a dense one), about four times slower for lack of 6GB.

Bottom line: For anyone whose models genuinely fit in 10GB, the used-market RTX 3080 is not just cheaper than the RTX 4080, it's a few percent faster too, since its wider bus gives it slightly more raw bandwidth. But that 10GB ceiling is the real constraint: it locks out 14B-class models and anything larger entirely, where the RTX 4080's extra 6GB is the difference between a native fit and a heavily offloaded fraction of the speed. Anyone planning to run 13B+ models locally should treat the RTX 4080's VRAM, not its slightly lower bandwidth, as the deciding factor.