Both my K60 and my K2 are Co2 models.
Differences:
different cylinders - forget interchangability
K2 has vented barrel.
K2 comes with a compensator (I took it off and installed a Nygord Comp).
My K2 is a short barrel version - recommended by Don Nygord. It uses both the short or standard cylinders (I have both).
K2 has adjustable rear sight (width of notch).
I can notice no particular difference between the two in the triggers. They are both very fine examples of the art.
The K60 is nose heavy to me and the K2 is not (some shooters like nose heavy).
Grips are different on the K60. I used to prefer them to what came on the K2. However, after shooting the K2 for a few months I decided I liked those on the K60 less. Either fits well - they are just different.
When I upgraded from the K60 to the K2 I also considered the two dominate APs - Steyr and Morini. Of those, I only really gave serious thought to the Steyr LP2. My reason was quite simple, only the LP2 has the more modern pellet seating mechanism found on the Pardini.
Would I make the K2 choice again today? So far as the gun itself, there would be no doubt. Without Don Nygord's support being available, I would have to give some thought.
I have been able to find the Pardini K2 listed on only a single website in the USA:
http://www.bauershooting.com/ap.htm
The price there is $930. Note that this is not the website of the Pardini distributor in the USA - who's website does not show Pardini APs at all.
Hence, if I was making the choice today, I would probably opt for the LP2 from our host. Good service would then be assured.