Different stocks and every now & then, the barrel.
Generally the difference between the PSS & VSS is the stock. Both are made by HS Precision with the aluminium bedding block. However, the PSS is fatter in the grip, wider and flatter in the fore-end and has a second swivel stud for the bipod. The VSS stock is more like a sporter stock and is slimmer and smaller and lacks the additional swivel stud.
Personally I like the VSS as it's handier to carry all day (yep, I'm either lazy or a sissy).
Regarding the barrel, Remington did offer a limited run of 5R barrels. That's the rifling patterned after the Russian rifling that shoots better than regular button rifling. 5R barrels are what Remington sells to Knight Armament for the SR-25 (AR-10 type firearm). I don't believe that 5R is currently offered.