If you turn on turbo mode then it will allow the CPU to raise the multiplier when more computing power and a single core is needed. This is not a permanent state and the CPU will drop back down when idle (or if all cores are being used).
Agreed with neon, it'll run at a constant 3.4Ghz (4 Core Turbo) or 3.7Ghz (1 Core) much longer than the rest of the components in the system will last. You only start shortening the lifespan of the CPU when OC'ing and using higher than stock Vcores. Even then, if you stay around 1.4V-1.45V, it'll still outlast everything else. The point: Don't worry about it, lol.