1. The Dropbox API doesn't have a particular speed I can guarantee. Your connection speed to Dropbox depends on the routing you get between your ISP and our servers, and may be slower than your ISP's rated speeds.
Sometimes resetting or retrying your connection gets you a different route and better speeds, but that is outside of our control. Some ISPs also throttle sustained connections so if you see an initial high connection speed followed by lower speeds, that could be the reason.
2. The performance of specific API operations, such as search, also can't be guaranteed as it will depend on various factors, such as the number of items in the account being used.
3. The Dropbox API does have a rate limiting system, but we don't have any specific numbers documented. It is only designed to prevent abuse though, and is accordingly relatively generous. Further, the limits operate on a per-user basis. That being the case, you generally don't need to worry about hitting it in normal use.
Also note that not all 429s and 503s indicate rate limiting, but in any case that you get a 429 or 503 the best practice is to retry the request, respecting the Retry-After header if given in the response, or using an exponential back-off, if not.
