I have a .25 Impact MKII and I'm still waiting for my pre-ordered .25 caliber, 700mm slug liner to get here. I also had a 600mm slug liner for my Crown and tested a variety of slugs, most of which shot very well. I think either the .25 or the .22 will serve you well, here are a couple of things to keep in mind and might help explain why you see so many more .22 videos and reports than you do the .25.
You see a lot more guys shooting slugs out of .22's for a reason. #1. Bob O posts a lot of pesting videos and he uses a .22 caliber. #2. Matt D. and the Airgun Hunters in South Africa also post a lot of videos. They shoot with .22's because they are not allowed to have .25 cal air guns down there in S.A.. #3. The .22's were released first, so there are a lot more of them out there being tested and used for videos than there are .25's. Many people just recently got their 600mm .25 cal. liners and still more are waiting for their .25 caliber slug liners in 700mm to arrive.
If you give it a bit more time, I think you will see plenty of people using the .25 caliber liners. I think the 700mm liner will be the liner that most .25 caliber Impact owners will want to own because it is most efficient and offers more power for the same amount of air. FX has just recently started filling pre-orders for the .25 cal 700mm liners, you'll see plenty of videos and posts talking about them very soon! I have lots of slugs from Dale at Varmint Knocker just waiting to get tested as soon as my 700mm liner gets here!
If you decide to go with the .22, there are plenty of people that can get you dialed in with the proper slug, velocity, tune etc... If you go with the .25, I tested 30+ different slugs and have comprehensive results on all of them with info on which shot the best at various velocities. I think you'll be happy with either! Good luck!
Stoti
