Even if you can overclock the HD2500 (I doubt it but I have not checked - AFAIK, all clock multipliers are locked on non-K), it is unlikely you would be able to overclock it enough to get remotely decent frame rates in any but the least graphically intensive games out there at medium-low settings.
Intel IGPs do not get remotely decent until the HD5000+ and even there, we are only talking about performance in the neighborhood of a R7-240/250.