I'm presupposing you want a rifle with irons. You may want to handle an UltraLux prior to buying as it has a looong barrel. The 452 has a somewhat better rear sight, but the 455 Lux has the new interchangeable barrels so one rifle can shoot different calibers.
I do know that the 452 Lux/Trainer had one action screw and one "barrel lug screw", but both are excellent shooters. The 455 Lux now has 2 action screws and the barrel is fully free floated as I appreciate it. I'm not sure about the action screw set up on the 452 Ultra Lux, however, but it may mirror the 452 Lux/Trainer set up.
One advantage of the Ultra Lux is that it is quite. I have heard some compare the noise level with subsonic ammo to a suppressed rifle.
I own 2 452s, and they are proven performers. The jury is still out somewhat on the 455. I hear the ones that have accuracy problems do well with bedding and headspace adjustments. Dan Lilja just completed a first run of drop in barrels, but I am unsure whether those "drop-in" to the 455 Lux. I've only seen one so far, on a 455 American.