Tuning Are all Stx barrels interchangeable?

I can’t speak specifically to the Wildcat MK2 since I don’t (and never did) have one. However, apart from the shrouds and excluding the new Crown/Dreamline SuperLight barrels) ALL current FX barrels are interchangeable. If the WC MK2 uses the same STX barrel system as the Wildcat MK3 I can confirm the interchangeability. I simply switch shrouds between my guns if I want to use the barrel on a different gun.
 
So after speaking with bigragu, it looks that everything is the same except the transfer port. The wildcat mk2 doesn’t have the little step on the end that helps locate the magazine in both the impact, and mk3 wildcat platform. Oh well. 
I wanted to do some testing between my 500 and 600 barrels, but didn’t want to take anything apart. Guess I’m in the market for a 600mm impact barrel kit. Thanks all for the help!
 
You'd rather buy a barrel kit then take things apart? Up to you of course but it only takes a minute once you heat up the loctite enough to smoke. After that I just put things together more or less hand tight. They don't move. 

You can also just do the connections at either end of the barrel house.(sleeve) and then you don't have to mess with the TP to stainless part connection just swap in both parts together.

Especially if you just want to try that length in that gun and aren't sure.
 
You'd rather buy a barrel kit then take things apart? Up to you of course but it only takes a minute once you heat up the loctite enough to smoke. After that I just put things together more or less hand tight. They don't move. 

You can also just do the connections at either end of the barrel house.(sleeve) and then you don't have to mess with the TP to stainless part connection just swap in both parts together.

Honesty, yes. I don’t want to strip the barrel in my wildcat just for testing purposes when it shoots so well. I really just wanted to see if the 600mm barrel would work for what I’m looking to do to increase speeds a little without sacrificing too much air. I don’t really need the compact setup of my impact any more as I’m now going to use it as a tripod mounted gun. I originally got it in compact for walking through the woods. This task is better suited for my leshiy. I want to set it up to shoot the king heavies at around 950fps, and maintain the shot count I have now shooting them at 930. I don’t mind spending the money to get a barrel, I just figured If I already had one, why not try that first.