I have the MSI FX890-GD70 and I would not recommend to use more than 2 GPUs inside a normally ventilated PC Case. I have 3x5830 and currently am running only two of them.

My PC is not a dedicated miner so I still wanted to maintain a "classical" setup of all the cards plugged inside the case (which is Fractal Design Define R3) and with plenty (2x front intake, 1x sidepanel, 1x inside to push air between GPUs, 2x exhaust) of 120mm Noctuas I reach approx 90°C on the GPU closest to the CPU (when every other PCI-E is populated - positions 1 & 3 & 5).

I am still scratching my head about how to utilize the 3rd and last 5830, but as I want to keep everything packed inside the case (the PC is in my "working" room), it gets tricky.