I've been doing a lot of this kind of thing lately as my morning warm-ups. Just 30-45min each, looking at a master work or photo ref and trying to pass a squint test just using blockbrushes. Hand-picking the values, no eye-dropper tool. As I've gone along I'm trying to push the suggestive language of the squares with some textured dual-brush settings. It's interesting to see what works and what doesn't. Especially in coordinating areas of simplicity and complexity.
They basically fall into 2 categories here, matching black&white, or mentally converting to black&white.
I know they're not much to look at. But they've been a great study already. The biggest thing is that it's all about interpretation/compression, and trying to capture a certain essence in the abstraction beyond a literal recreation. More to come.