You might be able to get 4.8GHz, it will take some trial and error. Overclocking past 4.5GHz will take some work. But your cooler should be able to keep the temperatures in a safe range. Your PSU should be fine.
It's cutting it close for extensive usage. Technically you should be fine, but your PSU is going to be 75%+ capacity when you load the CPU and both GPUs hard.
You might be able to get 4.8GHz, it will take some trial and error. Overclocking past 4.5GHz will take some work. But your cooler should be able to keep the temperatures in a safe range. Your PSU should be fine.
I honestly wouldn't do it, I'd look for at least a 1000W PSU. EVGA has some epic deals on their PSU's right now. Their 1300W is under $200 on Newegg right now! With an overclocked FX-8350 power hog and 2x290's I'd be more comfortable with a 1000W. I would probably upgrade my AX860 if I were ever to add another 780Ti, but since that will not happen, I'm staying 860.