Panasonic Lumix S5 II outperforms on sensor size and video (6K per RTINGS) while Ricoh GR IIIx excels in portability for street shooting. S5 II body weighs 478 g more but supports 70+ L-mount lenses. GR IIIx fixed 40 mm lens and 0.8 s startup suit candid work but limit flexibility compared to S5 II's IBIS and phase AF.