I'd go for at least 32GB+. It'll fit in 24GB but leaves you little to no room for context, and that's at 4-bit quantization.
If you want to run unquantized, you definitely need 128GB.
It also comes down to inference speed, not "can I run this". 8-bit quant is quite a bit slower on an M5 Pro.
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Nobody runs unquantized, there's literally no reason to. Q8 would be the largest anyone actually runs on consumer hardware for inference.