About every one that gets a 2X wishes later they had more power. Get the variable. You'll never regret it.
^What he said^
I got a fixed 2x Nikon on my first 460. Quickly swapped it out for a 2.5-8x Nikon variable. I kept putting the 2x on other guns/Encore barrels, but it kept getting replaced with more Nikon variables. It seems to have finally found its place on a Blackhawk, for now at least.
As for your question, I would recommend the 2.5-8x Nikon Force XR. I've found it works pretty well even in relatively low light, although I haven't exactly compared it to any of my rifle scopes. If you have a spare rifle scope laying around, go ahead and try it on the CVA to see how well you like having a rifle scope on it before you reach a decision.