Aren't V grade only used in high current applications of which GS-X does not need?
Btw, Nelson Pass is like a DIYer on steroids. Love what he is doing with his First Watt company as he is still doing essentially DIY on the side even though he is the founder of Pass Labs. Shows his love of the field.
I said "certain applications" and that does not include the GS-X, Justin already said that these JFETs run at Id of 1mA so even GR grade will do fine, there is not much point to go for a V grade, and then use a higher value source resistor to degenerate the Id down to 1mA.