There is a lot of discussion about the Brno Model 4 and its accuracy on Rimfire Central. Here are a few threads below.
h t t p s ://www.rimfirecentral.com/forums/showthread.php?t=533163
h t t p s ://www.rimfirecentral.com/forums/showthread.php?t=761073
h t t p s ://www.rimfirecentral.com/forums/showthread.php?t=550101
h t t p s: //www.rimfirecentral.com/forums/showthread.php?t=589264
There are many more threads, but these will give you an idea about what people are observing about the accuracy of their Model 4's. While these are anecdotal reports (and it's easier to make claims on forums than to back them up on the range), if there is a consensus of sorts to be drawn, it is that the Brno 4 is a better shooter than a CZ 452. This is perhaps not surprising as with its longer barrel it is heavier (more inertia and hence more stability), it has a wider forearm (again for more stability on the front rest), and it has a barrel tension adjusting screw which can help with accuracy when adjusted appropriately. These reports also suggest that while that the Model 4 is perhaps comparable to or better than an Anschutz 64 action in accuracy (and keep in mind there are many different 64's), it is generally not the equal of the Anschutz 54 or Winchester 52 or Remington 40.
Of course it's important to keep in mind that not all rifles of the same model will shoot the same. Some will be better or worse than others, while most will shoot typically for that model. In other words, two different Brno 4's may not necessarily shoot equally well. Another thing to keep in mind is that some Model 4 rifles may have seen a lot of use. The production dates for the Brno 4 are 1957 - 1973. Many of the older rifles may have been "refinished" or refurbished in Czechoslovakia or the Czech Republic before being exported to North America. Indeed many of the rifles seen over here seem to be older ones, although there is not necessarily anything wrong with them or that they are any less accurate. The refinished models have a kind of parkerized appearance, while the others are blued with the classic look, shiny and dark.
I had a Brno 4 at one time. I liked its design and solid construction. I liked its weight and the way it sat on the front rest. For what it's worth, my impression was that it seemed "nicer" than any CZ I've had. I didn't have it long enough to become very familiar with the barrel tensioning feature and perhaps if I had it would have improved my results with the rifle. In any event, I reallocated my resources when I bought another rifle.