Best 290x for oc?

[Super_]

I want to use them in sli. And also if I use 2 Gpus in sli and they both have a 750 minimum power supply requirement do I need a 1500w power supply?

 

[Dorosh]

Just to note AMD calls it CrossfireX - SLI is for nvidea.
The 750 minimum power takes into account "average" computer power usage for all components. So no, you don't need to double that number. Depending on the card, there should be information on the minimum required to have them in crossfire - it will likely be closer to 1000 - 1100 w.
If you're going to overclock - best to choose cards with larger heat sinks and the more fans the better. The lightning cards for example are good for that.

 

[ko888]

The Sapphire Radeon Tri-X R9 290X OC is a good choice. The maximum clock speed that you'll be able to reach is dependent upon the quality of the ASIC that is installed on that card.

For a system using two Sapphire Radeon Tri-X R9 290X OC 4 GB GDDR5 [SKU# 11226-00] graphics cards in 2-way CrossFireX mode a minimum of a 1000 Watt or greater system power supply is recommended. The power supply should also have a maximum combined +12 Volt continuous current rating of 72 Amps or greater and have at least two 6-pin and two 8-pin PCI Express supplementary power connectors. (Minimum system power requirement based on a PC configured with an Intel Core i7 3.2GHz 130 Watt TDP processor.)

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) is the most critical factor.