MJVandershonk: Please accept my apologies for the incoming wall of text, its a long reply and its also getting late here.
I just noticed that I didn't make it clear in the OP what I am wanting this pc for. Over 95% of the games I play are older off-line titles (battlefield 2, source engine games etc and the only multiplayer I use is over a LAN so I'm not looking to build a supercomputer for the latest games like overwatch and the like since I've no interest in them.
the main reason that I'm wanting a replacement machine is that out of the three computers I've got on the LAN, this one is by far the weakest. since I only use the LAN with my uncles and they are notoriously picky about what they play the pool of games which we play is extremely small. Since I set up the LAN in 2006 and they started coming over regularly some time after we have played a total list of:
Battlefield 2 and mods
Enemy territory: quake wars
Counter Strike:Source
CS:GO
Insurgency
Day of infamy
A 2 weeks long coop campaign of IL2 1946
company of heroes (1 month tops)
having picky uncles + very few games supporting LAN = very few MP titles taking my interest.
The reason I'm building a mid/high spec machine over a budget/second hand parts 32 bit one is that over time I have built up a semi-sizeable backlog of single player 64 bit titles (transport fever, superhot, satellite rain ect) which wont require a cutting edge system, yet greater than my current one. star citizen is still under development so the requirements will increase over time. this build should let me get into it, though not necessarily at top settings.
skimmie: Seeing what you want to do with it, an i7 CPU is complete overkill. You can play all that stuff perfectily wel at high settings (1080p) with an i5-7500 (or maybe even lower?), with Star Citizen the obvious exception. And even for that title the recommended specs are lower currently if you can accept medium/high graphics settings, from what I could find.
As for memory; for those titles, you don't need memory that's clocked at ultra high speeds either (though going for the cheapest (and thus, usually, slowest) possible memory is not the best idea either).
Also, since you mentioned you don't upgrade your system often, the mainboard you selected is a really nice board, but why do you need a Z170 chipset? Seems to me H170 (or maybe even B150) would be perfectly ok, and significantly cheaper.
See here for a nice comparison table (it's for Sky Lake, not Kaby Lake, but still).
And last, +1 for modular PSUs. I totally agree with the sentiments of the other posters.
Just my two cents ofc :)
thanks for the info.
regarding the ram, the lower speed ram at the time of writing is more expensive than the 3000mhz one (see my above post).
Thanks for telling me about those other boards since I didn't know there were other socket 1151 chipsets, I just happened to find that particular one amongst a small group I was interested in and compared it to the other features in asus's z170 line-up and it seemed like a good balance, I was under the impression that the z-170 series was a recently designed board ranging from low end budget to high end use, judging by the features offered.
Since I've already planned my build around it I'll stick with it but its useful to know about the others for future use since sometime in the future I may need to overhaul my other PC.
My brothers PC runs an older I5, sandy bridge I think. while an I5 would run all those things great, I do want a bit of future proofing. I've heard around the kaby lake series has been made windows 10 exclusive for one reason or another and since I'm planning on moving up to windows 7 I figured I may as well get something that will last a fair while (the i7). I might go to windows 10 eventually but I really hate the look of 8/10. if I do move to windows 10, kaby lake uses the same socket so there is the potential for upgrade if necessary, although I have heard there isn't too much difference.