One thing to take into accoount when using the Pet Calculator. On fresh tames, the calculator under-scores Int and Dex.
Try this:
Enter a fresh tamed Mare's data and note the score.
Now enter 125 for Int and Dex (because that is what she will train up to) and you get a much better score.
Now try a Cu. My fully GMed Cu has 258 Int and rates 4.4. If I change his Int to 290 (the max), he scores a 4.6. But what does a Cu do with Int?
I think all the big pets will train to at least 125 Int and Dex.