Load testing

It does depend on how you plan on load testing. If you are going to go the whole hog and simulate a variety of user scenarios performing different functions on the site

And from our experience (vested interest alarm: 50% of what we do is load testing: SciVisum ltd),

I'd suggest that this is kind of load testing is really the only type that makes sense.  It's all too common, for a company to do some 'simple' load testing in house; get some numbers that give them a false sense of security and then crash and burn as their site traffic goes up. 

It really does help the business, and the tech teams; to start off by defining the User Journeys that are the 'money making' vital routes on your site.

Then you can plan load testing to measure those: and the number you want is 'completed Journeys per second' for each journey.  (forget 'concurrent users' as a measure of traffic: concurrent users is not what your site is for! But to get users through the specific journeys).

With these kind of metrics, there's no risk of a false sense of security: because you're measuring the right thing.

The user journey/second figures  will be different for each journey (coz different things happen in the software/databases for each).

Once you know your Journey figures, you've then got hard data to show the bosses, in a language that they can understand! 

If any of the numbers are low: then you don't need to write a business case to justify work to fix it: the test results speak from themselves: and the decision whether to 'go with it as it is and take a flyer' or 'spend to fix it' : rightly rests with the management who hold the purse strings.

If you're planning to do a load test each month or more, then buying the pricey software tools and training up someone makes sense: otherwise it's way too expensive, and the software ends up as shelf-ware!

Performance specialists like us are often a more sensible way to go.

If you do go with consultants I would suggest http://www.acutest.co.uk/

Yup, they are good: not pure web testing folks like us though.  And if you want to talk to someone who just this month preferred us over them...