That rosewill PSU doesnt stand a chance. Since you got a crossfire capable board i would suggest something like the Corsair 750TX. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
If you arent planning to crossfire, consider something like the corsair 550VX http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Both of these are very good PSUs and will last you for many years, rosewill is not known for making good PSUs, the red switch on the back also tells me that it is an older design that doesnt have APFC. Your PSU provides at best 31A on the 12V rails, which is only 1A more than the corsair 400CX and you certainly wouldnt run a 955 and a 4870 on the 400CX even though it provides almost as much power.
whoops sorry i meant the 4870, brain got side tracked, however they both use approximately the same amount of power. The 4890 was a new stepping that could give better performance with the same power usage as the 4870, i just typed the wrong thing.
Rosewill is not known for high quality power supplies. Although there have been a couple of improvered models overall they are not high quality.
The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the 12 volt rail(s) can easily power a system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the 12 volt rail(s) can power a system with two video cards operating in dual mode. There are a few exceptions like the new ATI Radeon HD 5XXX series cards which use less power due to their energy efficiency.
A high quality 500 to 550 watt psu will have a +12 volt rail rated at 40 amps. A high quality 700 to 750 watt psu will have a +12 volt rail rated at 60 amps.
Corsair, PC Power & Cooling, and Seasonic are some of the brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty. Lately we've been seeing a few other brands offering some high quality units. An example would be the Antec Earthwatts series which is an improvement over Antec’s older series psu’s.
A good choice would be the Corsair VX550 that Hunter 315 mentioned.
Very good choice! Seems newegg screwed up the pricing scheme on those two again, definitely go for the 650TX in this case, it will even allow you to run 2 5770 down the line if you need more graphics power.