You already got my opinion on when to pick. Store bought tomatoes are picked on the green side and they are varieties that I don't care for. There are too many better varieties for the home gardener to grow.

Dean,

To answer your question, a counter-ripened tomato should reach the same overall quality (including pH) as a vine-ripened one. Once the seeds are fully formed in the fruit, the ripening process commences, and proceeds without any further cues or food from the plant, so far as I know. If you pick it grass-green but still mature (as they do for commercial harvest), then ripen it on the counter, it may dehydrate a little through the stem but it will still have the same pH and almost all the flavor. I'm convinced that a few of the flavor compounds are influenced by warm temperatures, such that the sunny outdoors activates more of the subtle ones than a cool kitchen, but that doesn't affect canning quality.

I think the "peak of ripeness" qualifier is to make sure that people don't can tomatoes that are past their prime. Overripe fruits lose their acidity and become less safe to can, but even green tomatoes are acidic enough to be okay (witness the recipes for green tomato mincemeat).

--Alison