I'm not so sure about Oro strengths being his fighting skills .. but rather his intelligence and wide knowledge of jutsu. His performance against the 3rd was horrible, he had to rely on summoned HOKAGES and long-range jutsu to stand a chance. And he was in a young body compared to the 3rd, who was in a VERY old body. No, I think the 3rd had Oro in mind for being a choice for Hokage because Oro is very smart and creative... and would make a great leader, if he wasn't so twisted.

Think of it this way .. Shikamaru would make a 100x better Hokage than Naruto (at this point in the story), because Shika is SMARTER than Naruto. Does this mean that Shika stands much of a chance against Naruto in a fight? NO, of course not, by all accounts Naruto would simply overpower Shika (unless Shika could come up with a miracle).

I think it's probably similar to the 4th vs. Oro .. 4th being more of a pure fighter, tons of chakra and heart, but not necessarily very bright. Oro being more of the calculating intellectual, who memorizes tons of details and knows psychology and manipulation very well.

EDIT : Summoning definitely is a measure of someone's ability, but certainly isn't a measure of someone's STRENGTH .. would anyone say that Naruto is stronger than the 3rd, simply because Gamabunta is a lot more powerful than the Monkey King? No, because that's ridiculous [img]i/expressions/face-icon-small-tongue.gif[/img] Summonings have their own powers and personalities, that cannot be measured purely as extensions of those who call upon them. And it is also clear that using human sacrifices to raise DEAD Hokages is a very cheap technique .. if Oro was truly strong he wouldn't have NEEDED to call them to just to beat up a VERY elderly man.

Oro = overrated