I would never waste 4k on a PC. 1.5 k to 2 k would be the highest I would spend but even that is pushing it. the other money would go towards a Xbox One and PS4 and pre order a bunch of games.

I would wait another year at least, and get a GPU with hdmi 2.0 output.
No point in buying that now and not being able to use it on a 4k projector at 60hz when they become affordable.

I would wait for DDR4 in spring ^_-

I wouldn't personally.

DRAM speeds have very little effect on CPU performance, especially when you throw in a cost ratio.
Plus DDR3 is only going to continue to become more and more expensive, it's already triple the price it was a few years ago, DDR4 isn't going to be any cheaper.

And on the flipside, Broadwell on the socket 1150 will either have a dual-memory memory controller where it supports DDR3+DDR4 where DDR4 will be supported on a revised chipset... Or a plain DDR3 memory controller.
Haswell-E will probably move over to DDR4, which is highly likely going to require a new motherboard anyway.

That's compounded by the fact that DDR4 isn't going to be substantually faster than DDR3 anyway, at-least initially. - The standard/basic speeds will probably be equivalent to a high-end DDR3 kit. (Samsung Green DDR3 modules overclock like champs!)

If i had $4000 to spend on a PC i would wait for the next gen GPUs and for a new haswell E series CPU from Intel so I could have an Octa core CPU and DDR4 ram and HDMI 2.0. Especially since my current PC has NO issues running any games on ultra at 1440p.

Meh... there is no challenge building this PC. Anyone can spend money and buy a massive powerful PC.

How about adding custom loop Water-Cooling or fitting all that spec in to an mATX build? Then we can talk what goes where and how...

to be honest i'd never spend so much money on a rig, and i rather have that feeling that i crafted something cool out of a somewhat constricted budget. with that being said, i can sign the OP's Rig, only that i would not use more than 1 GPU. because electricity bill. mine's way too high anyway.

The majority of the time a PC is in an idle state, when that occurs the CPU will enter a low-powered state.
When you're running multiple graphics cards and not doing anything intensive, the extra graphics cards are switched off. (AMD ZeroCore.)
Then the primary card also enters a low-powered state.

However, if you're doing a compute job, having faster and more graphics cards can actually save your power, the power increase from adding extra graphics cards isn't a linear increase due to how you can never get 100% utilisation out of every functional block in a GPU.
Then add the "hurry up and finish" ideal, where the faster something can be processed, the sooner it can power down and return to an idle/switched off state.

If for instance you had one CPU with a 95 watt TDP and a second CPU with a 95 watt TDP at load, but one processor was twice as fast, the faster processor would actually use less power as it can get to idle faster.

Power Supplies can have a fairly large impact on electricity consumption as well, the more efficient the less energy that is lost in the conversion.
I live in Australia myself, so my energy costs are roughly 20% lower than yours in Germany, so it's still expensive, but having a powerfull PC with 4 GPU's hasn't impacted my energy consumption to any great degree compared to about 4 years ago when I was only running 2 GPU's.

Oh thanks, i didnt know that, i thought that all the GPU's are trying to flex their muscles when heavy stuff like games show up. (maybe i really should get a second R9 270 then. :3 hurpadurp.)

if i had 4000 Norwegian Kroner to buy a PC it wouldn't have been a very powerful PC