The ProGuard 7 is the only oiled filter that I recommend because of the 7 layers of media. It really does filter well for an oiled gauze media.
Does it flow as well as K&N or similar cotton gauze with fewer layers? Probably not, but that's the trade off of having extra layers... . filtration will be MUCH better.
The AFE Stage II is known to whistle more than other intakes and it has been somewhat verified that the reason being is because of the large 6 inch intake opening in which the filter mounts on.