Originally Posted by pballer0303
Is there actually that big of a jump in performance between an upgraded valve and the stock one in my '99 autococker?
No... Though it depends. Since you want to run on CO2 12 grams, most aftermarket valves commonly available will not offer you any advantages. Quite the opposite in some cases.
There is nothing wrong with the Palmer LT valve linked above, but you probably don't need it.
I would start tuning with your stock valve and the stiffest set of valve and hammer springs from a madman (or similar) spring kit if you don't want to retrofit to the old Sheridan style springs.