I do not have a BRNO but do have a CZ550. I would go with the CZ550. Mag capacity in 458Lott is 5 in the magazine. Normally in the 458Lott they feed and extract well, no work need here. They are a lot of gun for the price. You can spend a little to tidy them up and make them very slick to a lot of money. I had my 2 CZ550 trigger lightened to 3lb and the hair trigger disconnected. They are very reliable.

I have not used a Kimber. I have shouldered them and they are a better fit and not as heavy. The stock is more slender than the CZ550 which from memory is heavier and beefier than the BRNO. So I can not comment reliably on the Kimber. I feel that as the stock shape is better for me the Kimber would have reduced felt recoil. I do believe they have fixed them up so you no longer have to play Kimber roulette.
Meant to add. With reducing the barrel length you will change the handling characteristics of each rifle, not necessarily for the better.