@Espinetenbolas:
If you lack power, don't do Crossfire… sell this card and buy a GTX1070 or a GTX 1080... multiGPU inventions have proven to be little or nothing practical for many reasons... and more so with the existence of much more powerful card models.
- 1. I come from another post saying the same thing. You have a balanced team, to play at Full HD even at higher resolution less at 4K. The 480 just came out so you just bought it. Enjoy it before considering a change. And if you see that because you use 4K, several monitors etc, you need more power… it's time to dig into your pocket and go for a Nvicia like the one the colleague indicates, the 1070 - 1080. And for me, they have come out at a price of robbery at gunpoint, so I would think very carefully before buying them, although everyone is free to dispose of their money as they want.
Configurations of two or more graphics cards depend a lot on the game. In some games two graphics can approach 80% more performance. But in other games or you gain very little, or it will only give you problems. Add to that problems with temperatures, the need for a quality power supply and quite a few W that will easily cost you 100€ or more, the higher consumption of the equipment = more expensive electricity bill, etc.
Personally, I only recommend using two or more graphics cards if it is done with high-end graphics cards and that is a lot of money in hardware. The AMD 480 performs similar to the Nvidia 970 GTX. Without being top of the range, it is a very successful graphics card, so enjoy it.