Splunk doesn't come as prebuilt appliances, you size hardware yourself depending on your needs. Splunk scales well both horizontally and vertically (= it will efficiently use the available hardware on one box, and it's easy to build clusters that share the load efficiently as well). So you could say that the EPS is what you want it to be, since you're the one controlling the hardware specs as well how many systems you will use.
This is some reading material to get you started:
http://docs.splunk.com/Documentation/Splunk/latest/installation/capacityplanningforalargersplunkdepl...
http://docs.splunk.com/Documentation/Splunk/latest/installation/SystemRequirements
For further inquiries, my suggestion is that you contact Splunk sales which will no doubt be happy to explain these concepts in detail along with how Splunk compares to other vendors and products like for instance ArcSight products.
