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.GM5 test data on DxO Mark G1X Mark II test data on DxO Mark
Wider, longer, faster lens than predecessor, with good overall optical quality; Faster AF performance; Closer macro shooting; Built-in Wi-Fi and NFC with remote shooting; Decent JPEG burst performance; Excellent build quality.
Localized flare issue when wide open; No real net improvement in image quality over predecessor; Slow burst mode when shooting RAW files; Poor battery life; Video quality is so-so (not like Canon DSLRs).
Great image quality for a tiny camera; Excellent high ISO for its class; Built-in EVF; Built-in hot-shoe; Improved ergonomics; Improved image quality for long exposures; Improved burst rate with hybrid shutter; 1080/60p video.
Slightly bigger than GM1 (but not by much); No built-in flash; Shallow buffers with RAW files; Dynamic range not quite as good as some competing models; Below average battery life.