340 or 440

right Aj but as you intimated you have to warm up the 400 or 440
here's the simple physics
lower compression requires more throttle to move vehicle
more throttle for given power == more heat and less gas mileage
light foot or no
unfortunately there is no simple answer short of changing pistons
open chamber heads use the special KBs
closed chamber heads more piston choices but D-Dish for daily driver/ street
more dish for towing or heavy car with tall gears (and iron heads)