I7 2600k oc

i am new to this field(overclocking). from whati have read, i think the intel have unlocked the k series ie multiplier can be adjusted. But at the same time won't the warranty be broken if overclocking is done.
also is a external cooler essential for oc 2600k(multiplier change to 40keeping the voltage and bclk at stock (100mhz)) if using a stock cooler is enough then what would be the max temp. or is it the other way ie does multiplier change, bring about voltage change automatically. need explanation guys.
apart from this is it better not to overclock if you are planning to use the system fora period of say 5yrs.(lifespan consideration) need help dudes.
gaming would be the most cpu stressing factor in my case and do gaming requires a higher clock, ie wont 3.8ghz(with turbo) be enough with today's games(with a decent gpu). also is turbo boost by default active or should we manually switch it on(motherboard does support turbo boost).
whats your opinion..

OC'ing the CPU for games is, strictly speaking, unnecessary. The 2600K will handle all games nicely, but there will be limits. Cranking the CPU to 4.5 GHz will give a performance boost, but the difference will depend on whether the game is CPU or GPU intensive. Cranking up performance (of the CPU) on a GPU intensive game will give minimal (if any) extra performance: for those games you want to OC the GPU(s).

I have OC'd my (2500K) CPU to 4.9 GHz, but backed it down to 4.0 GHz because the high OC is not necesary for my uses. I have even restored it to factory without loss for my uses.

If you are OC'ing on a regular basis an aftermareket cooler is essential. However, if all you want to do is prove that you can achieve an OC for a short time, you can use the stock cooling. But, do not keep the OC'ing long or run any stress testing without an aftermarket cooler. In all likelihood the rig will go into auto shutdown, but you do not want to risk your rig to prove a point.

The longest prospective lifespan for your CPU will be if you do not OC at all, and decreasing with the amount and degree of OC'ing you do. If you are not an ultimate gamer you can probably accept performance with yur CPU and a good GPU at high (but not ultra/max) levels of rez.

As you ar new I recommend that you use the OC'ing options in the UEFI as they are factory tested.