wombat13,
The .338-06 is a great caliber, and if it were my choice between that or a .35 Whelen I would personally opt for the .338-06 since I feel it is a bit more versatile especially for a re-loader.
As the owner of two Coopers, I can heartily recommend their products to anyone that is interested in them. I have been very pleased with both of mine, even though I did have an unusual flaw with my first one that Cooper made right no questions asked. Both of them shoot extremely well, and are generally the most consistently accurate rifles I have ever owned to this point in my life.
The Savage build is not a bad option either, and if you are mechanically inclined and have the right tools you can probably build a very nice rifle for similar or less expenditure. However, if you do not have the tools, or are not very good with your hands (I am all thumbs) a semi custom rifle made by professionals may be the way to go. From a sheer cosmetics standpoint I think the Cooper M52 action is better looking than the Savage action, not that my subjective opinion on looks matters that much.
Functionally the Cooper action is quite a bit smoother than the Savage though, and everything operates like the proverbial well oiled machine in the Cooper. The bolt travel is smooth, the lock up as you turn the bolt handle down is also smooth as it snugs in, rounds feed from the magazine like they are greased. Also of note are the very good extractor used on the Cooper bolt, and the pivoting fixed blade ejector that will allow the shooter to control how much ejection force there is. The Cooper of course is also a three lug bolt, which theoretically results in more even bolt lug contact and better consistency of lock up. While I don't personally put much faith in that it sounds nice. The bolt lift is also a bit shorter, but is also a bit stiffer too since you are camming the cocking mechanism in a shorter distance.
Plus everything else has already been done, the trigger is already excellent and easy to adjust for pull weight, the M52 I have was a bit over 3lbs and I reduced it to right around 2.5-3lbs very easily with only an allen wrench; Cooper includes instructions on how this is accomplished. No other trigger adjustment was really needed since take up, over travel, and sear engagement were perfect. I have never felt the need to adjust the trigger on my M57 since it is literally perfect for my use.
Also of note is the fact that the Cooper stock will already have been properly glass bedded to the action, and this is yet another step you will not need to mess with or practice up on.
Either way you go, your father in law will no doubt be completely stoked to receive a new rifle.
