Maximum effective ISO is an estimate of the highest sensitivity at which a camera can capture excellent quality photos.
Cameras with higher effective ISO will be better choices for indoor photography, night shooting, and indoor sports photography, especially if you intend to make large prints.
You can learn more at our glossary entry.
Maximum effective ISO test data courtesy of DxO Mark.A6300 test data on DxO Mark K-x test data on DxO Mark
Excellent image quality; Improved high-ISO performance; Better JPEG quality; Fast autofocus; Very good subject tracking with real-time live view feature; All-magnesium body construction; 4K video.
Slow buffer clearing (no UHS-II support); No touchscreen, Clunky menus; Wi-Fi can be a bit frustrating to use.