The only other gaelscoil I am aware of closer to the city is Gaelscoil na Deise, but I'm afraid I don't know anything about it. Perhaps someone else on here can comment.
St. Declan's is one of the larger boys primary schools and is as far as I know still well regarded, although you might want to check class sizes as not sure what they are like now. There is also Waterpark, haven't heard anything about it recently but I think it now takes on more pupils so class sizes are larger.
I suppose particularly if you were looking at the 2 schools in Ballygunner, you would feel pretty cheesed off, but I know from speaking to people who actually live in the direct vicinity of the schools, they have had difficulties getting there children in there since the development of the Dunmore Road/Grantstown etc has gone so nuts.