Personally.. I would go for the more up-to-date.
Being the GTX 580;
- Quieter etc..
When you SLI that in the future you will be more than happy.
The GTX 470 can get very hot, and the fan on it is very, very loud.
Then when you put two hot, noisy cards together there'll be even more heat and noise.
I'm sure a single GTX 580 will be cooler, more power efficient and less noisy.
I advise you to get the GTX 580, then SLI in the future if you need/want too. XD
Thanks for reading, Danny.
GTX 580s in SLI are hotter and consume more power than GTX 470s in SLI.
Would you advise him to get a GTX 680 and SLI those?