Sorry, what I meant with "recursive" was doing the recursion myself, instead of handing it off to a server like Google's DNS server. If I follow the replies starting from root server one by one, am I likely to hit some limit?
It seems unlikely that you were able to overload the Google public dns server, and it also seems unlikely that you were saturating your connection. Thus you probably hit a rate limit. If you go recursive, and cache at least the TLD servers, distributing requests evenly across the 13 logical servers that typically manage a TLD such as .com, you’ll probably see a much higher per second throughput than through the google server, but still constrained by rate limits.