<p>A classic ASP.NET app - AppSrv + MS SQL DB. Both servers are heavy-lifters 8 cores, 20 GB of RAM. When load testing, the throughput goes somewhere to 400 VirtualUsers (according to LoadRunner) with CPU being approximately 30% utilized an DB server primarily idling - response times go dramatically up, to the point of unresponsive.</p>

<p>The usual suspects, such as Max Pool being exhausted and conn limit on ASP.NET set are not at fault: Max Pool is set to 200 and about 80 conns are used; conn limit is set to 0. </p>

<p>I ran with ANTS profiler the code and it showed that Thread blocking did not contribute significantly. </p>

<p>Ideas very very welcome!</p>

Does the host utilize App Pool?
Did you try increase the number to 5 to 10 in
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An Application Pool -> Performance -> 
Web Garden -> Max Number of worker processes
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