A 1.125x FLUX speedup was real. The harder question is where diffusion gives back time.

In the previous post, I benchmarked training-free block-residual caching for 4-bit FLUX.1-dev on an Apple M5 Max.

The short version: caching helped, but it did not give me the clean win I wanted.

The longer version was more interesting. A fixed-interval cache produced real speedups, then failed a same-seed PSNR gate so badly that I almost wrote the wrong conclusion. The images were not necessarily bad. They had drifted from the uncached denoising trajectory. That sent me down the rabbit hole of metric floors, windowed SSIM, LPIPS, CLIP scoring, prompt stratification, and interleaved timing.

That work is here:

github.com/kkjcodes/m5-flux-block-cache-benchmark