I'm really bad about measuring fruit additions, and usually just wing it based on what's available. But I've used 1.5 small-ish pineapples in a 3 gallon batch (kids ate the other half). But this was in a sour beer, so I wasn't all that concerned about how much acidity it would add. More important than pH is the total acidity, and I suspect that it would have added too much acidity in a non-sour beer.
10 oz is probably not too much in a 5 gallon batch, but it wouldn't be a bad idea to pull off a gallon in secondary and dose it with a certain amount, let it ferment out, and taste the result. If you like it, scale it up to the rest of the batch, otherwise dose it again and see where you wind up.