The best GPU combination for $1,200

[DIV1D3]

Hi, I am wanting to get into mining and I have $1,200 to spend strictly on GPUs. I was thinking of getting 5 R9 270Xs, that's actually about $1,150 and 3 R9 280Xs which is about $1,100. I'd just like to know what is the best config of GPUs for $1,200, I don't have any heat or electricity limitations, only the power draw of max 1000W-1050Ws.