Graphics Card Help

[Ohms Law]

Im going to build a pc very soon. I honeslty have 0 experience but ive been looking at graphics cards.

http://amazon.co.uk/VTX3D-Radeon-7870-Tahiti-Graphics/dp/B00AM3A7JY

amazon.co.uk/Sapphire-11199-16-20G-Graphics-Display-Express/dp/B00A1572TQ

amazon.co.uk/Sapphire-11199-19-20G-CrossFireX-Multi-GPU-Technology/dp/B00A1572FK
These three are the same thing, but they have different outputs and dimensions
Someone help

 

[radio rahiem]

@2gunsup
@Liquid