Dang, only 32 A on 12v rails combined, that's rather gimpy for a modern 500w unit, i must say you should upgrade your PSU as well, since i've heard numerous complaint about Enermax PSU circa 05-08 before the introduction of Pro and Modu 82+ series, regarding their durability under consistent high load. That HD 4870X2 could pull 20 A alone on its peak load, while your PSU has stated that it has 20 A as the OCP of each of its 12v rails, so that unit is simply not adequate for its intended purpose.