Great! According to the spreadsheet, their web server needs to be able to handle around 208 requests per second. But if you run a load test on their farm, and you are given an Avg RPS, how many people can your farm handle based off the give utilization statistics? This was a bit harder to figure out, but eventually I got there. After plugging in the actual Avg RPS that the farm could handle while the hardware was still in it's "Green Zone" was 11. When you put that into the spreadsheet, the number of Total Users that should access their environment should be less than 1,320.
You can download the spreadsheet from here: http://sdrv.ms/Xp7Sq0