I5 4670k OC with Asus, seeking advice.

A aftermarket CPU cooler is always good.
Well, if you don't like noise than i wouldn't c anything wrong with it.
I truly dont know sorry

First, its never a good idea to OC a stock cooler. Stock coolers are designed to handle @ 5w TDP more than the stock CPU. That's heat. By OC to 4.2 you have added @ 40-60w more heat to the CPU, so if you did any intense CPU application, you'll see your temps skyrocket, possibly resulting I'm thermal shutdowns or even damage to the CPU.

Second, what manufacturers don't explain very well is just what those simple 'easy OC' do. By using that you have effectively changed your CPU buss clock from 100.0 to 103.? If I remember right number. This changes several things internally, not only the GHz of the CPU but also your RAM. You are only seeing it stable because the stock voltages are also bumped up to support this.

Instead of using the turbo-v to raise your speed, for 4.2 it is well advised to use the BIOS multiplier. Your CPU will run just fine on stock voltages with a simple bump manually from 34 to 42 in BIOS. With the Intel speed-step left on, you will see normal idle of @ 1.6GHz, and CPU will only ramp up to 4.2 when required. You are basically only raising the normal 'turbo' setting from 3.8 to 4.2 doing this.

Leave BLCK set at 100.0! All sorts of funky things happen when you fiddle with that buss clock multiplier.

Get a decent aftermarket cooler. Do Not be suckered into thinking that just because a cooler is aftermarket it is better. More than a few coolers are just fancy replacements for the stock cooler, and a considerable amount of them are actually worse.

If you are still not turned off OC, go get an education. There is plenty of info out there on this site and others like overclock.uk that can teach you how to OC and not only do it right, but also safely. The last thing any of us would want to happen is to see someone burn up a $200 CPU because of 'gimmick' software like AsusSuite Easy OC.

If you want to fiddle with OC a gpu, OC the gpu through the gpu software. Asus supplies a decent GPU boost program with the gpu. The 'gpu boost' that comes in the Turbo-V, is designed for the integrated gpu, not for an add-on card. If you activate the LucidLogix stuff and run dual graphics like me, then you can use that to bump up the integrated gpu for a better picture. Just do so in slow stages, only raising it by @10 keeping an eye on temps.

RealTemp, CoreTemp, Speccy are all good for Intel CPUs to monitor temps. Start with a stock baseline and go from there. Use prime95 small fft's for a program to punish the CPU. If temps go past @70 its time to back off voltages or OC speed etc.
Either way, 70 for CPU and 80 for gpu (furmark) should be your upper limits.

Prime95 and furmark will drive your CPU and gpu harder than any game out, so if you get those running acceptable temps, anything else you run will be better temp-wise, and safer on your equipment.

Doesn't hurt to have the EVO , but if your not overclocking the stock heatsink is sufficient.

Running the fan at 100 % all the time will be annoying for one thing. And it will reduce the lifespan of the cooler.

Heat is the enemy of electronics. It (47 C) may not be high enough to significantly reduce the CPU life span. I try to keep it as cool as I can.

The EVO will drop you into the 30's, and at stock speeds you should only get to the 40's or so with normal heavy usage