Overclocking can cause that sort of problem. In short, the more you overclock anything, the more you loose data. The more you loose data, the more you have to reprocess it. In game like FF14 that is inefficiently written, that can mean slower response rather than faster, despite the OC. Understand that things are rated at the speeds they are rated at usually because of (normal and expected) manufacturing flaws. OCing causes those flaws to stand out a little more. In most cases (most not all) this can be mitigated by keeping the OC'd things colder, but not always.