What is more powerful between 2 sapphire radeon r9 270 2gb in sli or a gigabyte geforce gtx 770 4gb? If it's the sli I will need a psu of what wattage? And this is my configuration: Asus z97-a motherboard / intel core i7 4790k cpu / cooler master haf 922 case / corsair vengeance 16gb ram / kingston hyper x 3k ssd / seagate barracuda 1tb hdd / antec psu (how much watts? (I don't want to overlock)) / cooler master hyper 212 evo cpu cooler. And do the sli is compatible with my motherboard?
first of all 2x r9 270 is not called sli its called crossfire..sli is for nvidia...
Two video cards sitting closely together in your case will draw more power, produce more heat, and produce more noise.
Not all games support SLI and Crossfire. This depends on your video driver, not the game itself. NVIDIA and AMD often update their drivers to include multi-GPU support for new games, but if one of your games isn't supported, you'll either have to deal with one GPU or tinker with your driver settings to get the game working yourself.
SLI and Crossfire can sometimes cause a phenomenon called micro stuttering that makes the video look a tad choppy. It can be particularly aggravating to some people, especially at lower framerates.
so its better to get a single strong card than sli or CF
and for crossfiring r9 270x you will need good 750watt psu