For Watch Dogs you will need a quite powerful system. The HD6670 you have won't let you play it, not even at 720p. My recommendations are:
- First things first, you must change your GPU. I recommend the nVidia GTX750, because Watch Dogs is a nVidia optimized game, so you will have less performance issues. And it is actually a quite powerful GPU for its price and it will let play many games in high resolutions. But now you need a new and stronger CPU. For gaming GPU is more important, but your GPU and CPU must have "the same speed". If you use a Celeron single core with a GTX780Ti, the Celeron will bottleneck the 780Ti and it won't perform as it should.
- If you don't want to change your AM3 platform, seek for a Phenom II X4 965 Black Edition (it should be cheaper now).
- If you want to upgrade to AM3+, look for a MoBo with the 970 chipset (as I told you and those MoBos are cheap) and buy a FX-4300 (the FX-6300 is not useful unless you have a more powerful GPU).
- If you want to upgrade to FM2+ (which is the cheapest and it's the newest platform from AMD), look for a MoBo with the A78 chipset and buy a Athlon X4 760K or 750K (both are cheap and perform better than the Phenom I mentioned).
- If you want to upgrade to Intel LGA 1150 (this is the newest platform from Intel), look for a MoBo with the B85 chipset and buy a Core i3-4130. That CPU is the strongest of all i mentioned, but it's also the most expensive (not by much).
Saludos desde México