The end caps have a lot to do with flow and cooling properties on IC's. If the end caps are not designed right then core size does not matter much. Poor design makes the hot air travel across the core uneven. The bigger the core the more you have to compensate on the end caps because there is a limited amount of room in the z. Need flow data, pressure drop data, cooling data from both to decide which one is better. I am guessing that ash's are better. More R&D has gone into them, plus Ash has 3 different versions. Ash claims only a 1 psi drop which is a bold statement! Someone with a flow bench want to test them?
