Lets start with some of the major differences.
1: The 5R has a stainless action and barrel. The PSS's action and barrel is standard.
2: As stated, the 5R has a 24" barrel and the PSS has a 26" barrel.
3: The 5R uses a 11.25 twist and the PSS uses a 12 twist.
Aside from that, other than some stock differences there isnt much else different.
Having used the old VSSF in 308 (12x and 26" barrel) extensively and the 5R even more extensively, I would get either again in a heart beat. Both far exceeded my expectations. These rifles are the reason I dont have a custom 308 despite the fact that I am a huge 308 fan and the 308 is my all time favorate caliber. They have both been concistent sub .5 MOA rifles, even at a full 1000 yards. I cant justify spending 2500-3500 on a custom rifle
when these 308's do such an amazing job for a fraction of the price.
If I had to choose between the 2, I would get another 5R. I felt the 11.25 is a perfect twist for the bullets I am likely to feed it AND it handles the 150's - 175's with great results as well. It is perfect for the 190 SMK. The 12x will work with the 190 as well but I feel the 11.25 does it better. The 190 was by far the best load I cooked up. It dropped the least, hit with the most energy, drifted less and on a bad day would shoot .5 MOA at any range excluding windy days where if it was a large group it was a horozonatal spread and even then a "big" group was very rare. I felt the accuracy was a bit better overall with the 5R than the VSSF. My opinion on that is that the shorter, more ridged barrel was a bit less whippy. The draw back was that with this shorter barrel, the premium accuracy loads were much slower than the 26" version. I know that mathematically you will only loose around 40 FPS with a 2" shorter barrel but logistically in the real world, it was closer to 150 FPS to get the maximum accuracy potential where as the 26" barrel yielded maximum accuracy potential at top velocities. For example, the 178 AMAX in the 26" was deadly accurate at 2700+ but in the 24" it was 2550. The 168 was best in the 26" at 2800+ where in the 24" it was 2650-2680.
During the development stage of my 24" 5R, I couldnt figure out for the longest time why I could get max accuracy at top velocities with the 26" barrel where at top velocities werent giving me the same accuracy from the 24" barrel. I tried every powder and bullet combo imaginable. Finally an old timer who was always watching me "blow" powder, after I expressed my frustration, told me that the extra 2" caused the powder to burn a bit differently and decreased the muzzle blast. With the smaller blast, it didnt smack the bullet around as much coming out of the barrel. So to get the same results from the 24" barrel the load had to be backed off a bit. I did as he instructed and found the maximum accuracy potential. Was he right? Or was it coincidence? Who knows, but it seems logical. Regardless, it worked.
Me being the accuracy nut that I am, I would rather loose a bit of velocity for even a little accuracy. This was the trade off I made when I sacrificed the VSSF for the 5R.
The choice is up to your son-in-law. Does he want stainless or not? Does he want heavier or lighter bullets? Does he want maximum velocity potential or max accuracy potential? Either will do the job for years to come!