Is core center a Windows based program?
If so, overclocking in Windows = bad. The BIOS is always the best solution and has the most configurations and tweaks possible, and ensures the most ease of mind when overclocking. NEVER EVER overclock the CPU or RAM via a Windows based program, if you are because you don't know how to properly configure the BIOS I suggest you step back from the entire overclocking process and do some reading as to how about overclocking through the BIOS.
As far as memory timings go, you want everything adjusted manually, automatic changes are always bad news and you want to be able to be in control of bandwidth, stability, temperature, voltage, clock speed etc. If you are using automatic or self dictated settings, again, step away from your machine and don't come back until you know otherwise.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w