Generator 2 psi gas line sizing

I'm looking at getting a 26kW natural gas generator installed, which will use either 290 CFH (Kohler) or 333 CFH (Generac) at full load. The natural gas company has been out and confirmed my meter & exterior regulator would be good for up to 600 CFH.

I have a new house, with a 2 psi 1/2" gas line (25 foot, 3 bends) coming into the house. Specifically, it is Counterstrike FGP-CS-500. It connects to another regulator and interior manifold that goes to all my other gas appliances.

Generac dealer wants to run a dedicated 3/4" gas line directly from the meter, but the other 2 Kohler dealers want to tap off the existing 2 psi 1/2" supply line in my basement to avoid trenching or running a gas line through my attic. I am leaning towards the Kohler because it seems like a more robust generator/engine.

The gas company thinks I need to upgrade that supply line to 3/4". The gas company calculated my load to be 510k BTU with the 290 CFH Kohler. They cautioned me that generator installers "don't really know gas."

I'm looking for feedback on if that is necessary.