We have 25 and 27 hp Kohler engines on all of our Lazer Z's and no problems. On the 27's we have the bagger attachment and no problems. Atleast the employees have never complained about a lack of power. We find the engines last about 2400 to 2800 hours before they are wipped out and usually change the motor for about $2,400.00. We are averaging 5 years on a machine with an engine swap.
Exmark makes a great machine and cuts beautifully.
Good luck with your machine.