I put the K-MAC kit in this week for my SRT, got the car alignment today the camber is much better at - 1.2 from -1.6, I was eating up my inner tire also had a lot of toe in at 2.81 and today at 0.33. Car drives straight, I will need to put some miles on it to see how the tires wear. This kit will give you some adjustments for camber but not caster, the K-MAC will do both with the lower arm bushings. I can not say witch is better but the upper arm change looks to be limited to camber only.
Removing the lower A arm bushings is a PITA with out the removal tool, and pressing in the new bushings requires a big press but then your done.
While your old suspension parts needed changing, it is generally toe that wears the tread more as opposed to camber
on a healthy suspension. I'm not familiar with Xfires yet but I tend to run, depending on the type of car and how it's setup, up to sometimes more than negative 3 camber -on the street with sticky tires. If I'm easy on the toe, there is very little inner tire wear. Does this also hold true with xfires with a performance alignment?