ran 850w on my sli 580s, i would recommend 800 or higher, two 570s on that psu will strain it to death, though for the price you could go with a single card that would outperform 570sli and not need a new psu (and get money from selling your 570)

To be fair, if you were into 3d modelling and used vray, the 5xx series kicks the 6xx and 7xx series ass in terms of vray compute versus cost.

A 580 is faster at vray rendering than a 780ti, for example.

The difference is higher for v-ray rendering too, but sadly v-ray rendering speed is pretty much ignored by virtualy all review sites.

Probably because less than 1% of their audience know what it is or does.

You're lucky to ask the right people then ;)

There is nothing better than AMD when the budget is limited. 280X is a great choice and should boost your rig considerably.

Still a shame, because no sites actually cover it, for people wanting to do it the markets a minefield of gpus that have unknown performance at the task.

Only this week i saw someone who had bought a pair of 780s for v-ray rendering, when for the price of just one he could have gone with dual or tripple 580 sli depending on new/used prices.

Might as well just get a new GPU. No point in having huge power consumption while also lacking features of the newer cards.

Depends on your budget at that point. Eurogamer posted a good article on the best GPUs for the money: http://www.eurogamer.net/articles/digitalfoundry-2015-graphics-card-upgrade-guide

Interesting why you think this is? Also what cuda programms are effected?

I have a 750 Watt PSU for my SLi GTX 970s. But they consume much less power than older cards, so I would say you would want at least 850 Watt.

I'd say you are better off just getting a new card and ditching the old one. The 900 series has been really good, they run cool, consume much less power but are much more powerful.

Interesting why you think this is? Also what cuda programms are effected?

There is at least a few sites that DO cover compute benchmarks and in your particular case the ones dealing with light transport simulation ... 

As for mining performance, everything prior to Maxwell on Nvidia's side sucks badly because of bad integer or memory subsystem performance ... 

AMD hardware has a good history on mining performance and the hashing benchmarks show for it too ...

All of that is in the past now since FPGA's and ASIC's are threatening GPU mining in general ...

I don't want to be that guy but from my own experience I would recommend going with Nvidia and here is why:

- Nvidia used to have better frame latency, that is a very important thing in your gaming experience. Notice I said used to have because I don't know the current situation, maybe AMD has improved in that department.

- Nvidia cards generate less heat and hence usually are quietier. Of course it depends on particular card, brand and model.