I have both windstopper and powershield softshells and definitely prefer Windstopper most of the time- but there are situations when a Powershield jacket will outperform windstopper. If you are going to be doing anything really high exertion powershield is a bit more breathable because it is not 100% windproof (my powershield jacket- an arcteryx easyrider, I know not very technical- has thick fleece on the inside but despite the added insulation still breathes as well as my MH Dragon made from windstopper). It is important to remember that windstopper is a membrane based fabric so that it will be far more waterproof over extended periods than powershield. So unless you plan to forgo bringing a hard shell completely (not recommended) either jacket will serve you well.

The Scorpion is going to be the only completely waterproof jacket out of the bunch and the only one with a powder skirt. The Alchemy is out right away because it doesnt have a hood (if you are looking for the most versatile layering piece, go with the Alchemy because it will be easier to layer since it has no hood). The Venta SV and Gamma SV will be very similar (they are only 15g different in weight). The Venta SV has Windstopper which is water resistant and the Venta SV has fully taped seams, while the Gamma SV doesnt have taped seams. I would say to go with the Venta SV.