I have to say please tell me this isn't a serious question???

If so, I apologize

- 850W PS is far from the best on the market (go for at least a 1250+W)
- Running 5 GPU's on 1 PS risks frying your MB/PS/GPU's

So no it is not recommended, 3 GPU's per 1 PS is considered "safe" for the hardware, and seeing how old those cards are now you would be using way more power than say a newer GPU.