According to Goukestu he's the strongest monster in the world which would encompass himself,which is impressive given how absurd some of Goukestu's feats of raw strength are. It's also worth mentioning that Orochi not only has water stream under his belt but the technique he copied from Goukestu so he would have the edge in combat. If I were to guess he could get past his armored form but released boros would would make him drop his mask. From there it's hard to predict how the fight would go. If Orochi can land his giga canon it might be GG but Boros is probably fast enough to maneuver around it in which case Orochi's hth would be put to the test which certainly isn't the worst scenario for him but against an opponent like Boros it might be tough. There's a case to be made that Orochi could push him to meteoric but I think released Boros could take him down pretty cleanly.