Welcome to AH and welcome to the Blaser R8, I always say Blaser is like a disease and can be very expensive in life!
I'm a big R8 fan & user, I agree with most of what BeeMaa said above, a kickstop reduces felt recoil a lot but does add a pound or so in extra weight to the gun. I did not consider adding a kickstop until I was moving up to a .416RM R8.
If you want a kickstop my recommended ideal configuration would be:
- Standard Professional stock (old style, not 2.0, non adjustable). Kickstop fitted.
- Standard Aluminum receiver
- Standard profile .375 H&H barrel with open sights fitted.
- for .458 Lott I believe it only comes in Selous profile.
My son and I have used the professional success thumbhole (non kickstop) stocks with standard profile .375 H&H for a couple of hunting trips, we found the R8 very shootable with recoil very manageable in this configuration. Remember you are not bench shooting while hunting.
The real question is can you manage the recoil of the new rifle you have purchased or do you start spending more money to change the stock and add a kickstop. I see that you also purchased a .458 Lott barrel, if it were me I would be using a kickstop if shooting the .458 Lott.
My .416RM with standard professional stock fitted with kickstop is very pleasant to shoot, the heavier Selous barrel profile of the .416 and kickstop add additional weight, I don't mind the weight.
Good luck with your new rifle.