I'll argue nicely. The RX4750 has more surface area, and therefore will flow more. The base is MUCH larger than your 9" filter, and the RX4750 will end up placed much closer to the cold air supply. Not to mention that the base of the RX4750 is ideally suited for not only IAT mounting, but for building your CAI out of as well.
The filter suggested above is a simple cylinder. Calculating it'* surface area is a simple matter. Not the 4750. Because it'* an oval tapered cone, it gets much more complicated, but the overall surface area (if I recall correctly from a vague memory of the math I did over a year ago) is.....****. Very hard to calculate, but it is indeed higher than a 9" cylindrical filter, and doesn't have the disadvantage of the air entering the pipe at a 90° angle. The 4750 is a tapered design that allows the air to enter the intake pipe at less than 90°, reducing turbulence and increasing velocity. Alot of thought went into it'* design.
The 4750 is a tapered cone that measures 8" across the base, AND has an X-stream top (end). You will be hard-pressed to find a better filter for several reasons, which is why it was so carefully selected and tested for our application.
The filter was originally designed for the supercharged Xterra market. When I heard of it, I contacted K&N about it, and was able to obtain a test unit.
Edit....found some of my old notes from way back when.....
Because of the tapered design, the lower portion of the pleats are spaced wider than a typical filter. This also allows for more airflow.
Think of it as HOW the air flows through it, and into the pipe. That'* the major advantage. A larger filter won't get you more performance, but it will perform LONGER between cleanings at a higher level.