Overvolt + overheat = degradation, the severity of which depend on how much and how long. If you keep it cool enough, most processors will readily handle increased voltage. However, provided he keeps his system cool and doesn't exceed common known maximum voltages for the cpu cores for 24/7 usage, he'll be okay with it for quite a while. Often it's the motherboard going up in smoke at the VRM area before killing the cpu. An intel i7 is not generally recommended at this time, for any budget-conscious buyer. If it's a more-money-than-sense built, then feel free to get an i9 9900k/kf/ks. It's very close to a new generation release for intel so best wait if upgrading the processor soon. But why, doing that, the gain don't worth it, and why seaching troubles, and always testing if its stable or not, it's stupid, just buy a good I7 maybe not the last génération, but its a way the best choice, for me i would buy the next I5 génération if it has Hyper Threading, and for sure the K one like 10 600K to be sure to have the best performance and a cpu that will last for a longer time, and i'm also pretty sure it will handle all the games for maybe the next 10 years. (in case we still here gg), take care.