I know this is an old link but still a valid current question, Especially if you are going with a "knock off" intake.
Start with the flange size you need then I recommend you go as large on the body of the filter as use can ...more area means less restiction. There can be problems with SRI filters hitting the fog lights if you are equipped. K&N has a page that spells out every dimension of thier filters (Round/Cone/Oval Etc.)
(since I do not have enough posts I can't post links.... so copy and paste without the space between the ht & tp and the w & ww)
After measuring the tiny crappo filter that came with my intake and inspecting where I had room to "Grow" once installed, I decided on the RU-4450. The Typhoon uses a slightly larger Cone filter the RU-4960. But I went with the RU-4450 to be sure I cleared the fog light.