Web service testing tool supporting multiple request/concurrency

I need to test web service. Looking for a testing tool that might support the below requirements:

1) Need to execute 100K+ individual and different requests. This is not load testing. I need to see the responses of each request. 2) Capture the Success/Failure, response time and package size of each response. 3) Responses to be exported to external file system. 4) Ability to load the tool with thousands of new request 5) Ability to control concurrency - run 1 request or multiple request at a time. The number of concurrent request should be configurable.