most likely it's overheating. That 48C under load right? U haven't oc'd alot so I doubt it's because the cpu or ram wouldn't be able to take the increased load, u could try increasing both voltages if u want to, but I doubt it's going to help.
U could also try putting the ram on a divider or increase the latency. This would mean that it would be running slower, but this way we will know if it's the ram. (and if it is then that must be some really cheap ram, my cheap ram can take 220mhz (original 200) without any problems and this is really the cheapest ram I could find)