Here is a question then.... in my past lives with cars I have found that the OEM GM air boxes NOT the filter element was the restriction in the air flow. I had proved this many times over at the track and on the dyno by running full OEM, OEM box no filter and then no airbox at all. What I found was that with or without a filter element in the box, the car performed the exact same. However, if I removed the box I would pick up about 3 tenths in the quarter mile and about 15-20 HP on the dyno depending on which car we are talking about.
That being said, if you are looking to just have a filter than you can take out and clean versus just popping in a new paper element then you are probably on the right track. But if you are looking for performance you might want to take a look at replacing the airbox or removing it altogether, maybe put two small K&N cones on there. I personally dont know how they would fit since I dont even have a xfire yet.
Another thing to consider is that you are spending about $100 for two filters then you have to factor in the price of the cleaning kits which is around another $20-$25 IIRC. What do the paper elements cost at Wal-Mart? $7-$10 each? And how often should they be replaced? every 20k miles or so? You do the math here.
You also have to keep in mind that the K&Ns filter better as they get dirtier because they are a more open weave design than a paper element and rely on the dirt sticking to the oil to then gather more dirt and effectively increase the filtering capability as they age, that is said in so many words on the K&N site itself. Also, many people tend to clean the filters too often, not to mention they over oil them and that oil gets on the MAF which then screws with the readings that the ECU gets and the car runs like $#!T. Oh and back to the filtering part. On other boards people have had oil tested and found it to be consistently dirtier when running K&N and similar filters because of their more open design letting more dirt get through.
Just some food for thought. Until I actually get mine and take a look at it to see if I can replace the airbox with some cone type filters I can't really pass judgement, but I would recommend running just the paper element if you plan to retain the factory airbox.
Jeff.H... out.