Price is likely the same.

i5 4460 is almost RM 800 now, the cheapest H81 mobo is around RM 220 while RAM between DDR3 and DDR4 is basically the same.

A locked i5 (non overclockable officially but overclockable "unofficially" via BCLK overclocking) on a Z170, are you planning to overclock the CPU? If yes then you have 2 paths, one with BCLK overclocking (i5 6500 is the best choice here due to higher base clock), another one is the 6600K which supports overclocking officially.

GPU battle - this one has to be decided next week because the review and benchmark (official one) of GTX1060 haven't released yet (19th July), but from the current info that we have, GTX1060 is more worth in money.

CPU cooler can be dropped to save cost if you aren't going to overclock the CPU.

Generally will affect CPU only since Z170 mobo is made for overclocking but non-K CPU isn't.

Light BCLK overclocking is fine, if you are looking to squeeze out another 1GHz in the long run on non-K CPU then you better get a K CPU, it is more suitable for heavy overclocking via multiplier.

First, check if your Z170 mobo model has the non-K CPU BIOS update released or not, if yes, update it.

Locked CPUs have their multiplier locked down by Intel, meaning you can only increase/overclock the speed via BCLK, it depends on the stability of the CPU (lottery time again) and the temperature, I won't recommend going over 4.2GHz though.

Beware that overclocking via BCLK will also affect the speed of other components as well such as RAM speed.

My main usage is mostly gaming,
main reason to upgrade is for DDR4 and GPU upgrade and SLI only.
if that whut sifu said maybe i just go for GPU upgrade only.
thanks for advice~

Everything is fine.
Not so worth if you need to spend a lot for this upgrade.

Not all games show significant performance gain with high speed RAM, going from 2666MHz to 3000MHz will probably give you extra 5 FPS in average only, if you are gaming on 1080p60 and already have stable 60 FPS in game, then I don't think that 5 FPS will bring any changes to you.

For browsing, you can hardly feel any difference. As for rendering, yes if you render a lot of high resolution videos/graphics as the memory is faster (I/O) to feed the CPU with the resources it requests.

Assuming you sold your current RAM at RM 250+/- and you will need to top up nearly RM 150+/- for 3000MHz, are you ok with it just for the extra 334MHz? If ok then you can go for it