Game mechanics of the swords and attack power are not what they would be lore wise, Artorias would be able to do at least 30 - 40 times the damage he does in a real Lore based fight in both pure and Corrupt forms, Just because in game the cleansing greatshield blocks only 80% blah blah doesnt matter, Lore wise before Artorias became corrupt they were overrun by abyssal creatures and In a last attempt to protect his best friend and Companion Sif he put up the protective barrier to protect him, The fallen Artorias then became corrupt by the power of the abyss, Increasing his strength through the mounds of humanity that lives within the abyss, Now the lore doesn't state that Artorias ever lost his wolf ring. Though it does state that Before the overrunning and defeat, Artorias had lost his Silver Pendant which was created to fight off the powers of the abyss. Though Injured, The corrupt Artorias had always proved to be a terrible enemy for any being to face and after some time of terrorizing the town of Oolacile, Finally he had been Finished off by the Chosen Undead after emerging from the abyss.
In light of information given I would say that though Artorias may have had his shield it still managed to somehow become broken by the abyssal creatures, which means Artorias would sooner or later lose himself to the abyss and become corrupt either way. In my mind the advanced power of Abyssal Artorias would make him a terrible opponent towards Pure Artorias due to the Abyssal Artorias would know exactly what Pure Artorias' abilities are seeing as he was once that. He would work around the armor, Shield, and Pendant to beat the pure Artorias in one way or the next, Be it over powering himself in Darkness by draining the humanity of the abyss to give himself more strength and possibly heal himself of damages or otherwise, Though this is Entirely my opinion and I am open to anything anyone wishes to say about it.
As long as it doesn't start an argument