Guys, I have struck a weird one:

I have a borrowed cpu here, from a forum member over here, he got it up to 5700 or so 2C/2T for pi on air cooling, so now Im testing it on single stage but something isnt right. In normal testing I got it passing running 32m pi at 5000mhz down to 1.320v but it locks up at 5100. The only way I got it to run at 5100 is to disable internal PLL override, with it disabled I got it up to 5600 but while its disabled I cant get it to pass 3D at any clocks. What the hell is going on?