Pc experts help me! (Graphic card VRAM)

Think about the future, there are other differences besides the VRAM.
Whatever you can afford, but I would pick a 6600K + 1060 6GB over 6700k + 1060 3GB

Pick a non-K 6700 instead. You can save money by doing so and the performance gap is really not worth talking about. Also, the 6700 has TXT and consumes less power than the 6700K.

Depends on your monitor resolution, if you run mods, if you plan on VR, etc.

Arma 3 specific benchs
http://www.ocaholic.co.uk/modules/smartsection/item.php?itemid=3957&page=4

TL;DR
<= 1440 3G OK if no mods or VR
=> 1440 6G with mods or VR

-Intel i7-6700k

Go with an i5 6600K instead of an i7 6700K, unless you're doing graphics/video editing or have a job where you need to do a lot of heavy calculations in general. Use the price difference to get the 6 gb card. If gaming is what you're going to use your PC for, the processor is the wrong part to splurge on, the graphics card is where the difference is made.

my advice about graphic cards :

don't buy the best of the market, why??? easy, they are expensive and all the games can run at maximum whit a less powerfull graphics card.

i always do the same whit my PC
1-invest a lot on CPU and motherboard
2-buy a very decent graphic card
3-buy new a very decent graphic card 2 years later
4-repeat the process 2-3 all time until your PC die or 8-10 years passed

whit that you will save money and you will get always will play at maximum graphics the games.

GTX 1060-3GB is NOT a 1060-6GB with only 3GB
They kept the same name on purpose...

Thanks Nvidia for their great naming skills

I'd go for i5 + 6 GB GPU if your PC will be for gaming mostly. I7 for video editing or 3D rendering.

My GTX980 hits 95% of its 4GB running Fallout 4, which is not a very demanding game. Pick the 6GB one.

Get the 6GB version of the GPU and ignore anyone telling you to downgrade the CPU.
If you can afford the 6700K and a Z170 - GET IT.

Unless you're on a tight budget, my advice is always get the best you can afford when you can afford it when it comes to building a new PC.

More VRAM = More detailed textures (generally)

3GB may not be enough to get high/ultra settings on some games. I'd get 6GB just in case.

I can't help You, I'm a horse.

1) Don't buy an i7-6700K for gaming.

2) Get an i5-6600K instead.

3) Get a GTX 1070 for the money you saved.