Automated Performance Load / Testing Tools

A group in my company is reviewing several User Load Generating testing
tools.   The selected tool would primarily be used for performance
analysis, but potentially could be used also for regression testing and
functional testing.  The candidates have been reduced to Loadrunner and
Rational.  Does anyone have any real world experience (positive and
negative!) using these tools in an AS/400 environment?

Thanks in advance,  Bill

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