I would leave it at 40.
If you ever replace the unit you probably would then have to have 40 amp breakers for the majority of units out there.
Also since the unit will draw 30 amps you want to have some leeway.

Note the above also depends on the wire gauge going to the unit.
A 40 amp breaker should have 8 gauge copper or 6 gauge aluminum.

I would also use some anti oxidant compound on the aluminum wire connections.