Potential upgrade path choice

[hmminteresting]

So I have an interesting problem. I built my PC 3 years ago. At the time of building i equipped my PC with 8GB or RAM and an i5 4690k. At a later date I upgraded to 16GB of RAM from klevv (llike its really good RAM at 2400MHz). However nowadays I need an i7 for running simulations and for battlefield 1. I seem to be getting fps drops in that and often when running simulations for businesses i experience hangs. I was gifted an MSI phantom laptop equpped with an i7 so I've been using that but I would like to use my pc for more than word proccessing and simple stuff. The problem I have is I need an i7 but should I:

a) get an i7 4790k which is still priced at £300 in the UK for a new one or around £250 for a second hand one that I trust

 

b) get an i7 6700k which is around £280 and will require me to buy a new mobo for around £90 (I'm looking at the Gigabyte GA z170 HD3 DDR3) with DDR3 support which will mean reduced features compared to my MSI z97 gaming 7. Or get one with DDR4 at a higher cost for new RAM as well

 

c) get an i7 7700k which is £329 and a new mobo and new RAM also I'm running windows 8 and apparently kaby lake doesnt support that so.... I'll need windows 10 which is something I dont want. Like AT ALL

 

options b) and and c) will cost more, but is more worth it in the long run. Also I have windows 10 on my laptop I HATE IT!!!!

Also theres the issue of all of this extra hardware I'll have lying around. I still have the original 8GB of RAM that I replaced. I do want to build something like a media PC but thats nowhere in the near future

[PenPoint]

a), especially second-hand one.

[DocSwag]

First one definitely. There are large risks with running ddr3 on skylake and Kaby lake that you shouldn't get into and the performance difference will be minimal. It's like an extra £100-200 for 5-10% extra performance, max.

[pagani123]

just get A. The other two would cost a ton more without a massive gain. 

[hmminteresting]

Okay thanks guys.