This article argues that local-AI performance on Macs depends on memory bandwidth, not CPU cores, GPU cores, or the Neural Engine. Using a simple formula (bandwidth ÷ model size × efficiency), it shows a 2021 M1 Max outperforms a 2024 M4 base chip by over 3× on a 7B model. It recommends buying used Max-tier machines and highlights lineup quirks like the M3 Pro’s bandwidth regression.