You already have the neros. If your happy with them I would save the money and just add to them vs replacing them.
I've never used an orbit so can't comment.
Maybe take a look at the Tunze orca. They are pricey but Tunze powerheads are very long lasting IME. With the sweeping motion of the orca a single one can replace at least 2 fixed power heads. Bonus is they don't sit against the glass so it makes glass cleaning much easier. They come with a 5 year warranty and customer service has been stellar. The 6075 version on one end and your neros on the other end or in the back would probably give you plenty of flow.
