I could have done that if I hadn't sold the other Tikka. The Tikka #3 does so well I won't be messing with it. But yes, I am done testing and Center-X did perform the best. But again, it makes me wonder just how well this barrel could have shot if it had a tighter fit between the shank and receiver. I'm talking tight without a .003" shim.You could swap your current barrel to your other T1X and see if it's the same fitting. Maybe you did get a 1-off bad product. Have you done any more testing? Is Center-X still the best for your IBI?
As for setting the headspace without a gauge, my method is inserting a loaded round "to ensure the rim is not crushed" into the chamber, you may have to use a wood dowel rod or other object to fully seat the round. After that, with the bolt closed and cocked insert the barrel into the the receiver until it stops. That's how I set my headspace and it seems to have worked pretty good.
A headspace gauge is recommended and I may end up getting one just to eliminated the danger of using a live round. In the end, everyone has their own method for setting headspace. Right or wrong, this is mine and I know it works.