I'm not even comparing their old age because neither was at the peak of their power at that point. Maybe Danzo was because of izanagi, but no way was Hiruzen. In their prime Hiruzen was superior. Danzo even said you were always one step ahead of me. Rivals aren't always equal and I see that happening with Naruto and Sasuke as well.
I believe Naruto will be the strongest in the end. He still has several potential powerups to get in taming the kyuubi and combining kyuubi mode and sage mode. Sasuke's only potential powerup left is the rinnegan, which Naruto has already fought against and beat albeit with help.
By rivals i dont mean equal, but the other never loses by a land SIDE. Its always close.
As for naruto, althogh i believe he would lose the fox, lets assume he doesnt and kishi somehow lets him combine two strength's that massively contradict each other. That still isnt a powerful up because sm and km are really the same. The user gains an increase in strength/power and chakra, therefore combining those two just increases the advantages it gives the user.
Obviously the side abilities of sm being able to sense other people's chakra. Similarly km gives the ability to sense evil thoughts/feelings.
Basically both are more or less the same. Combining them wouldnt make much of a difference.
Sasuke has more potencial and ive already explained why in another thread. He right now is the most complete ninja alive from konoha. Unliek naruto he has mastered all forms of ninja art. With his genuis and sharigan, he like kakashi could copy/master 1000 techniques which isnt far fetched. He can improve on his genjutsu especially tsukuyomi.
Tobi promised him a tailed beast, which i doubt he'd get, but if tobi keeps his word and sasuke becomes a jinchuricki, i cannot see anybody beating him. The only weakness sasuke has is his chakra, which isnt that low. Also from what i can see it seems the ems makes life easier for the user to use ms technqiues thus the decrease of chakra consumption acquires