We (blocket.se) are hitting almost 1b/mo and I can assure you that it's irrelevant wether the average p/v per second can be handled by some basic hardware or not. During peak hours it's an order of magnitude difference. Worth mentioning though that we are tightly focused in only one country, and probably have larger variations during peak hours than stack overflow does. I'm not sure what our traffic looks like combined with our other local sites.