I went with the 9", but it didn't fit the way it was supposed to. I have a really wierd shaped MAF pipe, so it didn't allow me to position it the way it is supposed to be (under AC lines). So on the end of the MAF sensor, I put the elbow piece on and aimed the filter straight forward towards the front of the car.
I think the filter was like $50 from Kirbans. I got the MAF pipe used, but Kirbans chrome piece sells for around $80. You should get a good fit if you buy as a package instead of piecing it together like me.