There is a good reason to buy a CZ 452 in whatever configuration you like rather than the CZ 455 and that is the 452 is supposed to be discontinued -- although new ones do appear from time-to-time. The CZ 455 will always be available, at least for the foreseeable future. The conventional wisdom over on RFC is that both the 452 and 455 should be equally accurate, but many are buying 452's for the reason outlined above. The conventional wisdom also has it that the Varmint model in either 452 or 455 is no more accurate than the American model with its thinner barrel; these are sporter, factory-made rifles, after all. If you can find a 453 model, the one with the single set trigger, you might want to give it serious consideration, as they, too, are increasingly hard to find.
The main advantage of the 455 is that you can switch barrels to .17HMR or .22WMR very easily. If you don't plan on getting a different caliber barrel or, as has been previously suggested, getting a Lilja barrel for the ultimate in CZ accuracy, then get the 452.
My own experience is mixed with the 455. My first CZ was a 455 American which I could not get to shoot very well. I needed to get a new barrel and have the stock pillared and bedded to get it to shoot. I also have a 455 with a TH stock with both .17HMR and .22LR barrels and it shoots without problems. I have a 452 American which is terrific as are my 453's in Varmint and Lux models. Some folks don't care for the SST but it gives you a "hunting" trigger and a "target" trigger all in one.
Just remember that ammo always makes a big difference when accuracy is important.