Enable the logging for one of the servers, and get a count of non
coalesced events for the server for 24 hours or longer and average
that down to EPS using 86400 seconds per day
(Number of events per day / 86400 seconds)
you could run this for a series and graph out averages, spreads and
standard deviations if you like.
Take either the one sample day or average of days, multiply by number
of servers to add assuming the same logging workload. I always try to
round EPS to nearest 100,1000 or 2.5K for purchasing reasons. I also
like to add 10% for bursting.
example:
one server was 90 EPS average
(90 EPS average)x(10 servers)=900EPS add 10% 990EPS, round to 1000 EPS.