OP, they're very similar. Most of the differences are not significant, despite what some might say. Here are all the ones I can remember:
The
open sights on the 452 and 453 FS and Lux are tangent sights instead of the buckhorn ones on the 455, which is a lot nicer in my opinion.
The
actions on the 455 are prettier and slightly higher quality.
The
trigger might be slightly better on the 455. (but throw a yodave or Rifle Basix on either and the difference is irrelevant!)
The
barrel on the 455 is pinned, instead of threaded like the 452. In theory, threaded is better, but I haven't heard any complaints about the 455's accuracy.
The pinned barrel allows you to
swap calibers: the 455 allows you to swap between .17 HMR, .22 LR, and .22 WMR in the same action, not to mention use Lilja barrels
The bolt on the 452 has two
lugs; the bolt on the 455 has only one. Again, two lugs is theoretically better, but I haven't heard any legitimate complaints. These are rimfires, after all: you barely even need
one lug
The 452 Lux has a
schnabel foreend: the 455 Lux doesn't have a proper schnabel.
The 455
only uses 11mm
dovetails: I believe some of the 452 had different dovetails, which would be really annoying if you owned a few, and needed different rings. (edit: some had 3/8" dovetails)
Some of the 452
editions haven't been released yet for the 455. If I remember right: the Supermatch, Silhouette, Style, Ultra Lux, Trainer, and single-set trigger Lux... possibly some left-hand editions too. Likewise, there are new 455 editions:
single-set thumbhole, Tactical Trainer, and the Evolution.
There are a few other cosmetic differences like the torx-screws. More details here in this picture-filled comparison thread:
http://www.czfirearms.us/index.php?topic=32042.0