The vast majority of reference 58xx's will hit 950-1000core with ease (I have owned 3 and all hit 1000 with the best stable at 1050). The vast majority of non-reference boards will not hit such speeds. Even the voltage moddable ASUS and MSI non-ref designs struggle to match the "classic" 58xx's for overclocks. That's what happens when manufacturers cut back on costs and use cheaper components.