I would believe its all in the OverClocking 

Performance RAMs can have tighter timings thus making clock cycles faster and improve performance? Something like that la... just like you, I am still learning abt RAM overclocking too

i think this is the simple EXPLAINATION
most Value RAM cannot go higher FSB ,TIGHT TIMING and HIGH Voltage
but Performance RAM can Boot UP Easily..

correct me IF I"M WRONG