In my thinking if you have an SL and an Evo, you don't need a Proto at all. By the same token, if you have a Proto, you don't really need an Evo and SL.
Seems you obviously want a Proto no matter what. I'd get rid of the SL. I'm adding an Evo this year and rode Proto last year.
They are all pretty close on the spectrum these boards.
That was the other part.. They are definitely close.. You are keeping your Proto I'm assuming??