soapUI 1.5 introduces simple and powerful SOAP LoadTesting functionality allowing you to:
* Validate a Web Services performance under different Load scenarios
* Maintain Functional validations to see that they don’t “break” under load
* Run several load tests simultaneously to see how they affect each other
Add Assertions to a Load Test – soapUI allows you to add LoadTest Assertions to LoadTests just as to Functional TestSteps. When creating a LoadTest, soapUI will always add a TestStep Status Assertion for us, we will add a TestStep Max Assertion to validate that our TestCase never exceeds a certain execution time.
Thys Michels Blog 
Good blog entry. Thanks.
BTW, look at another open source project (TestMaker) to run those soapUI tests in a grid/cloud of test injector machines for load and performance tests. A tutorial on how it works is at http://tinyurl.com/yzar9yz
-Frank Cohen
PushToTest
Can I achieve followed load generation in SoapUi.
Run each set of messages through the system with messages injected at constant rate of 172 TPS
message size320k
message size 2: 640k