[EDIT]
Ok gww according to my buddy here what I said above is wrong.
His explanation to me was that Solar panels are strange critters, and sometime they do not behave the way you think they might.
He also says that if you add an 80v string to a 90v string on a charge controller. The charge controller would probably drop to 80v, and take current from both strings. I think you could test this easily enough couldnt you ? Then he says that if you run odd panels in series. The current may / may not be the lowest panel current for output. Lastly, he explained that mixing panels is still not a good idea.
Yeah so my bad, I had never seen this phenomena before personally. Have always matched panels to run in series. Id be interested in knowing how the 80v and 90v string in parallel behave output wise. The math says you'll lose 70W(ish), but I know that does not always work out like that. So, give it a try