My old system used a 20 x 25 x 4 filter... I think that was the best available 15 years ago. My new ClimateMaster TEV049 unit has the slot for a 2" pleated filter and the air coil is about 28x30. It was installed with a nice large box on the return so I have good airflow across the entire coil... and old 20x25 filter feeding box from the top. So, I guess I have the option of using the 2" and just removing the 4" 20x25 if I want to... 20x25 = 500 sq in of filter at 4" pleat depth, as opposed to 840 sq in at 2" pleat depth. Any recommendations on which one will give me best filtration? Best air flow? Best all around combination of air flow and filtration?