Building GF a PC (Sorta)

[Beazel]

So, I was looking into building my GF a new gaming PC. Figured I'd spend $600, and get a mid-tier machine. However, this naturally led me to consider building myself a new PC and giving her mine. Here's the thing, my PC is relatively recent:

4690k
GTX 970
16GB DDR3 1600

So, what I'd be looking at in terms of a new PC would be:
6600k
GTX 1070
16GB DDR4 2400
Cost: $1100ish (w/ new power supply, HDD, case, mobo, etc)

Now here's my question; Would upgrading my system to this new system really let me see any benefit? Would it future-proof me? Primarily gaming at 1080p 144hz at the moment. Or do you guys think I'd be better off building her a $600 rig and saving the $500 for down the road?

 

[LookItsRain]

6600k wont give you any noticeable fps boost, just put a 1070 in your current system and build one for your gf

 

[Beazel]

6600k wont give you any noticeable fps boost, just put a 1070 in your current system and build one for your gf

Yeah, here's the thing, if I put a 1070 in my system ($400) and gave her a 970 - I'm still going to have to buy a competitive CPU, mobo, power supply, case, etc etc. By just buying the 1070, I'm already at $400 and by the time I get everything else, I feel like I'd be close to $800-$1000 anyways (partially because a good CPU for the 970 would cost $200 anyways).