Well, moving up to a 4gb card, with everything else the same, means you can run at higher settings without losing framerate. So instead of medium settings/50fps you would have high settings/50fps. If you want higher settings AND higher framerate then you need a card with more than 2gb vram and it has to be a faster card too.
The 1050 Ti has the extra memory and it is faster, but my concern is you will be paying around $140 for a card that isn't $140 worth of extra performance over what you already have. You can mitigate the cost by selling your 960, so it might not be too bad.