Tough call. My Antec Earthwatts 500 could not cut the mustard with a 4870x2 installed. Just couldn't do it even though I only have one Sata hard drive, one sata optical drive, and a Q9550 with no case fans. (Just the single 120mm case fan attached and that's it) On a full load my computer would trip the Antec's safety mechanism and shut everything completey off, making me have to switch the back of the PSU "On and off" before restoring power again.
Check your 12v rails with everything up and running on your MB in the bios when you start up. It should be under "PC Health / PC Monitor" depending on what Bios you have. Nothing should be under 11.5 on that screen regarding anything on the 12v.
Like mentioned on other threads I posted on, I had to get a Seasonic 650w S12 for my main rig and put the Antec on my backup rig, which is now running fine with no issues. If I were you, I would at least be looking at a 600w name brand PSU for the 4870x2. It's a gigantic PCB coupled with a huge cooler, so it's a monster on on power requirements.