Look at the targets that are available when one decides to purchase a CZ.
The proof is right there in that they will both be very close .
While these targets prove that they fire they also show the inherit accuracy CZ builds in every firearm.
The factory test target is a test for function rather than accuracy. It is not an indication of how accurate a particular rifle will be.
To the best of my knowledge, the barrel is the major difference. The stock is inlet differently to allow for different mag well and magazines. I'm assuming the 455 Varmint uses the same action screw setup as the 455 American, both screws on the action itself as opposed to the 452 which has one on the barrel dovetail and one on the action.
I have a 452 Varmint, it shoots very well indeed.
I'd recommend buying a 452 while you still can, I doubt you'll ever have any trouble selling it if you want to. I believe the 455 will be available for the foreseeable future.
The advice given by Chilly807 is very good.