The OM System OM-5 outperforms the Ricoh GR IIIx in versatility and stabilization per RTINGS and DPReview tests, with 7.5-stop IBIS versus the GR IIIx's 4 stops. The GR IIIx excels in portability with its 262g weight and APS-C sensor but lacks the OM-5's weather sealing and 4K video. OM-5 is the stronger all-rounder for most photographers needing flexibility.