Standard has one major advantage over the Pro - the second heat exchanger.
When the shocks are brand new they aren't terrible or anything on the STD. They aren't rebuildable though.
Pro is like 10 lbs lighter if that is an issue for you. (Hollow jackshaft, lightweight rotor, less bogie wheels, only 1 heat exchanger, etc)
Pro taper bars are awesome on the Pro. (Some hate them though so I dunno)
The console on the Pro has the buttons for the gauge rather than being up on the bars. I really like that as I have cracked the old style gauge cluster on my 2007 RMK.
Pro comes with ice scratchers, std does not.
They will perform virtually identical out in the backcountry. The Pro will have a slight advantage for the bumps on the trail with the Walker Evans. Standard has a big advantage for low snow cooling efficiency. The deciding factor for me was the fact that you can't buy a 163" standard.