The main reason the flat piston works so good is because you can get quench and a nice flat flame front that can travel very good. I mean which would you prefer to have say 11.0 comp with an open chamber head and a pop up piston or the same 11.0 comp with a closed chamber head with quench and a flat piston ?? Of course the flat piston with quench will be the better as it wont have anything in its way of the flame front that a pop up piston would. The main reason for the D-dish piston is to have quench and a pump friendly comp of about 10.5 and lower. So I would think the flat piston with quench would be best. The D-dish will work fine since part of the piston head is still flat for quench but as I said if you dont need a dished piston to drop comp then most go with the flat piston which I believe will have the best flame travel. I was going to go with flat pistons and quench but when I decided to use 75cc heads instead of the 84cc heads I had no choice but to use a D-dish piston and still have 10.6 pump friendly comp and still have quench. All said I believe the flat piston will work best. Ron