There is no way to limit the response to a specific number of results in the current API. There are two potential workarounds (neither offer a perfect solution):
1. As discussed in the other forum post mentioned, filtering on existing fields can narrow the results, but it would be hard to get a precise number.
2. You could ask for all results (or a filtered subset) and identify the specific number you want from the records returned, but that's not ideal from a performance and processing perspective.
This is good feature request and has been captured. I'm assuming the primary use case is pagination. If there are thoughts on additional use cases we would welcome them.