I've been recently putting the search engine project through it's paces.  I know that searching for Type A entities return in ~50ms (nice) but Type B entities return in ~1-2 seconds (ouch).  Having said that, I know why - the database query for Type B is horrendous at the moment.  The schema is changing drastically anyway so no point in putting that effort in now.

So I ran it via WAST and got some pretty decent results back.  While it does the job, there are obviously better tools out there.  And some of these can be expensive.

I've had a go of WAPT and been really impressed.  The trial version only allows 20 concurrent users, but you can do all sorts of things such as ramp up over time, specify random delays between 'clicks' and so on.  While my application is primarily AJAX, these are just treated as your run-of-the-mill HTTP requests.

At the end of it all I get a neat report, including interactive charts, which let me see when it reaches the maximum amount of throughput before it starts to decline.

With just Type A entities, it just keeps those pages coming.  With Type B entities...well, we know we have to improve!