I would think you want more than "zero lift" at speed, as you need enough lift to keep the airplane flying (unless you're airplanes have no mass to be lifted into the air?). I would also think the "ideal" angle of attack would depend on the given segment of flight (IE..in the straights, turns, ect).
Gary in the above is absolutely aerodynamically correct. In order to fly straight and level with a 3.75 lb airplane you better have 3.75 lb of lift. If if it's zero you have an RC car at best! The incidence is difficult to calculate because you must factor in the actual airfoil data, the speed, the mass and the low Reynold numbers involved. Most of the faster current airfoils are symmetrical and therefore have a no lift at 0.0 deg. incidence, not like the older MH17 airfoil.
When I was messing with Q500 airfoils I used Xfoil for analysis. I never looked too much at Martin's MH series as the NACA 65012 and modifications of it had less drag at Q500 speeds and Reynolds numbers. By the way the MH17 also has a more negative pitching moment that you must over come with the horizontal stab which translates to more drag. But never the less my conclusion was that you needed a smidgen of positive AOA in the wing. If you set up at zero wing and tail you would need to carry a slight amount of up elevator in order to force the AOA for the lift required. One might argue what's the difference in carrying a little up or having incidence in the wing or negative incidence in the tail? I would guess not much except maybe cleaner airflow over the tail if the elevators not deflected all the time. Plus if you force the entire airframe to move with the elevator you're also changing the thrust line of the engine as well as the wing.
It would be interesting to find the actual AOA of a Q500 pulling through a hard turn at pylon one. It would be tough because of the rate of change in relative air flow. It obviously doesn't go past around 12 deg. or it would snap when the wing stalled.
But it sounds like you are well into solving your issues.
By the way, from the photos above it's a great looking airplane.
SD