i want to get into pc gaming and i wanna get a good gaming pc so im building one and i need to choose between the 690 or the 780 { probably down the line gonna go sli} i am a very big fan of physx and game stream frm the nvidia shield and i will be using singe monitor at 1080p so can u plz tell me which one is better based on these details and plz explain why cause im a real pc noob