Depends on your hardware. I only have a GTX 250 at the moment, which isn't the best video card. But livestreaming doesn't depend on video card, luckily.
Nope. It mostly depends on cpu, ram and internet speed. E.g. if I only had a 2mbps upload speed, 2gb ram and a 1,5GHz dual core cpu, the quality would get really shitty.