Performatrin Ultra is not the same as Performatrin senior or any other performatrin for that matter. Both the cat and dog Ultra made it into the whole dog journal.
Honestly there is no comparison between Perform ultra and Science diet. Read a bag of SD and try and find some real meat.
I think it really is sad what happened to you cat and we all know that this was more of a family memeber then a cat :-( So you are probably really questioning anything you did different.
As a breeder I have my puppy owners sign in my contract that they will not feed SD. We do feed mostly raw to both cats and dogs. We do have kibble on the side also.
I think you did the best you could for your 4 legged friend .