You can set the size of the REST batch using the option headers:
Field name
Sforce-Query Options
Field values
batchSize is a numeric value that determines the number of records returned for the query request. Objects for children are calculated by the number of entries for the batch size. For example, in relationship queries, multiple children can be returned to the parent string. The default value is 2000; minimum 200 and maximum 2000. There is no guarantee that the required lot size will be the actual lot size; This is done to maximize performance.
Example
Sforce-Query-Options: batchSize = 1000
Docs: http://www.salesforce.com/us/developer/docs/api_rest/Content/headers_queryoptions.htm
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