Regarding your question: 13B 2_K seems to be on par with 7B 16bit and 8bit. Not much of a difference between all those. (Look at the perplexity values. Lower is better.) The second link has a nice graph.
Most people don’t go as low as 2bit though. It’s considerably worse than 4bit.
https://github.com/ggerganov/llama.cpp#quantization
https://github.com/ggerganov/llama.cpp/pull/1684
Regarding your question: 13B 2_K seems to be on par with 7B 16bit and 8bit. Not much of a difference between all those. (Look at the perplexity values. Lower is better.) The second link has a nice graph.
Most people don’t go as low as 2bit though. It’s considerably worse than 4bit.