70 Calories of chocolate is about 11-12g of (70-85%) dark chocolate, or 12-13g of Milk Chocolate(1). Chocolate's LD50 is approximately 1000g/Kg(2). So basically your body weight in chocolate. It's the theobromine that kills you, same as dogs, but they're much more sensitive to it. And it strongly depends on the kind of chocolate, pure cocoa is much higher in theobromine than milk chocolate: So 5 oz of Cocoa powder ~= 8.6 oz of Baking chocolate ~= 26 oz of Semi-sweet ~= 27oz of dark chocolate ~= 59 oz of Milk Chocolate ~= 3583 oz of White chocolate.(3) (White chocolate has no cocoa powder in it, just cocoa butter.) Note that these comparisons are of just the theobromine content, not the the 'healthy' stuff in chocolate.
I have personally tested this back when my metabolism was young by eating 2 pounds of Hershey's Kisses in one evening with no ill effects. :)
I don't think we know that much about flavonols, quercetin is the most studied and most of the studies used a 1000 mg/day dose, but I don't find any info about a most effective or maximum dosage.(4)
The reason to eat chocolate is cause it tastes fucking awesome. If you're trying to eat it for your health I feel sad for you. ;-)
"~70 calories of straight cocoa powder" is what the parent comment says, not 70 calories of chocolate.
That's an odd way to measure it though. Maybe they meant grams. If they didn't you have another battle because the calorific content between brands of cocoa powder varies wildly 70kcal may be as little as 17g, or as much as 40g.
...What's the maximum number of heart-healthy flavanol doses?