During those chapters... naruto has been done by like XXX amounts of scanlation grps... after TW quit and before Inane started... in those chapters some of the information provided is false...

In the manga... the scanlation people called mangekyou sharingan just plain mange sharingan until it was later proven wrong.
This 8th level thing is also part of an error that the scanlation people made. but since we all read the same type of naruto scanlation there is no way to know whats what unless inane release better scanlations of those chapters

Edit: oh and about the chidori vs rasengan thing... I think rasengan is stronger based on the water tower thing.. but if they both hit it will cancel out.

I wonder will jiraiya try to do a hybrid.... rasendori or chisengan or chidorirasengan... That would be mad hot!