Depends on what your primary propose for the rifle will be. It's been my experience that heavy barrel models of the same rifle are inherently more accurate (from slightly to moderately). They are more rigid and are less susceptible to things like vibration and barrel whip. The longer barrel will increase velocity allowing you extended ranges in certain circumstances. Also the actual shooting of a light gun is mechanically more difficult at longer ranges because of the light weight, it is more influenced by things you find difficult to control.
If this is going to be a carry gun that you stalk game with and shoot offhand or from sticks in a quick setting, there's really no reason the XS7 shouldn't be similar in accuracy to the VH. With a lighter rig thats faster handling and like you mentioned, is less likely to get hung up on brush and terrain in the bush. But if this thing is wearing a bipod and/or will see significant time shooting longer ranges off of a steady platform, the VH model will come into it's own.
As far as stocks go, I'm not sure what a "Cobb Job" is, but opening up the stock to accommodate a thicker barrel isn't very difficult. Any competent gunsmith will have no problem with it, the action and magazine is the same. Even if you get the XS7 you will want to go through the stock and open it up to free float the barrel anyway.
