@Misty
Thanks, that fixed it, I had stupidly downloaded 4.7 :-P

@Zev0
Where in the render settings do I set it to use my GPU's?

I have two nVidia GTX460's, bit crappy by todays standards but two of them were lightning fast with Octane (though sadly it will only access the RAM of one card as Octane doesn't add together the RAM of both cards).  I've got a viewport render from IRay, but it's a bit sluggish, I think it must be using the CPU and not the GPU's.

Trouble is, I can't find CPU/GPU settings anywhere, help! :-D