1.4v won't affect the lifespan in any significant way, it is the point where lifespan will start to reduce VERY minimally, if you go 1.45v for example it might last say 14 1/2 years instead of 15, but as long as you cool it effectively you'll be fine, nothing to worry about.
I say set it to 4.7GHz 1.4v and let it go, that's a very stable setting I use as a straight overclock on clients builds with 6700ks all the time, and it is always stable.
@Feardom, 1.5v or high 1.4s is where lifespan really starts to become a consideration, but you should easily be able to get a 4.8GHz OC on about 1.42 anyway, mine's currently at 1.41.
It is not catastrophic, your PC won't go up in flames and there will be no damage even if you do apply a bit too much voltage, you can just turn it down when you're finalizing.
It is a bit daunting at first, but its relatively simple once you get down to it.
The only damage that could really come about is having an insufficient cooler like the stock cooler and trying to apply a huge overclock resulting in overheating, or running Prime95 for 48 hours straight on a cheap air cooler.
OCing is a relatively safe and easy procedure provided you know what you're doing.