Why concurrent user metrics are no longer good enough
Take two different scenarios; firstly 10,000 concurrent users visiting your home page which is fundamentally static and delivers mainly cached data or 10,000 concurrent users browsing, searching and checking out from your site.
Although both scenarios represent the same level of concurrent users, the stress each scenario places on your app and backend systems is clearly very different. Testing how your site handles thousands of concurrent users will not give you an accurate measure of how it will cope with genuine traffic levels and real users performing activities across your site.
Understanding metrics such as the number of orders or quotes per hour your platform can handle whilst delivering an acceptable user experience gives a much more accurate and reliable indication of the true ability to handle peak traffic.