Speculative decoding on a 16 GB Mac: a 20% win that becomes a 25% loss

A 1B draft model speeds up Llama-3.1-8B by 20% on an M3 — at num_draft_tokens=2. Push that dial to 4 and decoding gets 25% SLOWER than using no draft at all. Here's the measured curve, and why low draft counts win when decode is bound by memory bandwidth.