The "Large" deployment described in the linked document will (in our testing) support between 2000 and 4000 events per second. Rough specifications are provided in the same doc, so I'm not sure what I can add here. Bottlenecks for LEM tend to do with storage IOPS (LEM writes to the disk constantly in a busy environment, so poor IOPS will hurt the LEM) and memory in the virtual environment. This is why SolarWinds recommends reserving the memory for the appliance, and treating LEM as a real-time application.
I'll leave ito actual customers to describe their experiences with reliability and stability: SolarWinds Security Case Studies | TechValidate