126GB is way to small and even 256GB will fill quickly. Plus you dont want it too full as it impairs performance. Just stick your favorite 4-5 games on it. I used mine to put BF4 on for quick map load times and it's a vast improvement over an HDD, EVE-online for if it ever (very rare) crashes whilst fighting, I can get back in on server quick enough that my ship is still alive. It has windows and all drivers on as well as virus checker and malwarebytes. Just stuck War Thunder on and seem a bit faster. Waiting to get ARMA 3 on there as well.
So 256GB for now. And when they come down in price for bigger SSD's over the next year or so get a 500GB+ size one if you need it as storage for other regularly used software.