Personally, if I subbed out Cascade for Citra, it wouldn't be oz for oz. Citra is a great hop but can flat take over if used in equal amounts with other hops IMO. I would use 1/2 (or just over) the amount that you used for Cascade. I'm sure it would work either way though.
In my brewery, I find this to be true when the beer is fresh, but as it ages a slight amount (say 3-4 weeks in a keg), the Citra domination seems to calm down so I can find the other hop varieties.