To me personally, that would make about as much sense as doing all of the tests in one gun and then expecting them to work in another one.;)
You don't say what the round/case/caliber is but the case volume in a pre-fireformed case is different from a fully formed case, and pressure is probably going to be very different because you typically fireform with a slightly reduced load. Then when you have the fireformed cases you are probably going to try and load to an increased pressure/velocity. Isn't the increase the reason for the larger case or are you just wanting to improve a case design and still shoot what would be the same ballistic load in the improved case?
When I fireform cases I have fun and get in some long range practice but to each his own.
Then I use the newly formed cases and do the load workup.