(moving to the Rules category as this question is not related to websites)
There are limits that apply to both the REST API, and to the Streaming API. In the case of the Streaming API, the limits are the 1% volume of data; numbers of filter terms that can be used; and on number and frequency of connections.
xAuth is not recommended for new applications, and has no influence whatsoever on the rate limits applied to an application.
You are free to request elevated rate limits via the Platform Support Forms but this is very rarely granted.