I have the cp-e, and it is great. I have never had any concern with water entering the intake, the filter sits right up under the headlight so you have to go through a pretty deep puddle to ingest some water, you can also get a water repellant pre-filter if you are worried.
I would stick with a dry filter over an oiled if possible, aside from the oil affecting the MAF argument, the filter is prone to a lot more dust in the location and oiled filters seem to clog up a lot quicker.
I am not familiar with the k&n, but I do know that the cp-e MAF housing has air straighteners and is identical diameter to stock, so there are no adverse effects to your fuel trims.
Nearly all men can stand adversity. But if you want to test a man's character - give him power.
Abraham Lincoln