No such thing really, if you want ram that wont limit your overclocking with ram in sync get ram rated at a higher speed then defaults, eg get DDR550 instead of DDR400, buy yes OCZ allows higher vcore and speeds usually.
The bios will have some ram ratios to drop the ram speeds when overclocking (and pushing ram with it) but to stay in sync with the high speeds rather then lowering ram ratios (or just increasing ram bandwidth), buy ram rated for higher speeds (try for some DDR500 or better, branded) to give sufficent head room.