I have a Nano and an Infinite Theory.
I think the Theory is on the same level as the Nano or close to it, so I would not see a need for having both balls in your bag.
From what I have read the Infinite theory will probably give you a similar reaction as the Victory Road. With the Infinite Theory being a little stronger.
So I am not sure that you need either.
However since the Infinite Theory is a hybrid coverstock you could make it a little strong and it might not be a bad ball for the in between ball that yo uare looking for.
So far I love my Infinite Theory, can play many lanes, with many different lines. I have not been able to use my Nano as much as I would like just because it is so strong.