There were some benchmarks a few years ago from, IIRC, the people behind either llama.cpp or Ollama (I forget which).
The basic rule of thumb is that more parameters is always better, with diminishing returns as you get down to 2-3 bits per parameter. This is purely based on model quality, not inference speed.
3-bit 27B will almost certainly be better. 4-bits is usually the limit below-which you start to see more steep drop-offs, but you also get diminishing returns above 6-bits. So I'd still rather pack in more params at 3-bits.
The basic rule of thumb is that more parameters is always better, with diminishing returns as you get down to 2-3 bits per parameter. This is purely based on model quality, not inference speed.