I just went through this same decision, 455 vs. 452. I read, talked to folks and milled over it for several weeks and decided on the 455 Lux. The 452 Trainer was the second in line but made my decision because I prefer the walnut stock of the 455.
22lr reaches it's highest velocity out of a 16-18" barrel, depending on the load of course, and a longer barrel will slow the round somewhat. I've seen quite a few claims that a longer barrel will give more consistent velocity between rounds but I have yet to find the measurements to back any of the claims. Maybe someone here has or can link to measurements?
The Yodave kit comes with springs to make the pull lighter and also shims to take out creep. It sounds like the trigger on the 455 is a slight bit better when both are stock but, still needs a work over to get working to liking. No big deal IMHO, is a cheep and easy fix.