How much is too much? I turned my 27 up to 4600 out of water and turn 4300 in the water by myself.

That's fine.

First issue you will see is the valves floating. Spring pressure on the stock briggs will allow the valves to float in the 4300 range. Kohlers are in the 46-4700 range with stock springs. After that most would say push rods or connecting rods and you CAN have issues north of about the 46-4700 mark with both of those things on both of those motors. There is folks who push them that hard or harder that haven't really had any issues other than occasionally bending a push rod which is not that big of a deal. Cheap fix and usually goes before anything catastrophic happens like a connecting rod failure.

Nothing is certain, but you should be fine with your setup. Run it like you stole it!

Kohler is a great long life motor with minimal problems