Which i5 is best for gaming with a gtx 970?

having a friend that wanted me to suggest a computer build for him however im missing out on which cpu in the i5 series would benefit greatly with a GTX 970 Graphics card..
im thinking about the i5 3.5gh...
thoughts?

depends which one. there are a bunch of i5's out there. the ones that have the most performance are the new current i5's. which is the found on the Skylake processors. the i5 6600K. the overclockable CPUS have the most performance cause you can push the clocks farther than non-overclockable CPUS, that run at stock speeds.

Firstly, don't go for the 970, the R9 390 is the same price, beats it in 9 out of 10 benchmarks and has twice the VRAM.
As for the CPU, what i5 he should go for depends upon his budget and whether he wants to overclock.
If he wants to overclock, go for the 4690k.
If he doesn't, got for the highest clocked i5 available in his budget.
Note that if he wants to overclock, he needs to have a Z97 motherboard too. Otherwise, save some cash and get a H97 board.

Also, if he's going to be streaming/editing video etc. it'd probably be worth him getting a xeon instead. There's some quad core socket 1150 xeons that are hyperthreaded around the same price as the 4690k. The hyperthreading'll help a lot in the aforementioned tasks (video editing and streaming, among other things), and you can use them on cheaper, H97 per se, motherboards alike how you would with a non-K series i5 as I mentioned above.

i5 6600k + 970 gtx + decent nonegimicky motherboard.

Nope

6600k seems to pricey what about a i5-4460 to match with the R9, i might have to persuade him to go R9 since im getting one in my build to, but hes read from a lot of unreliable sources on other forumns that the gtx 970 is better
(less power consumptions etc.)

if he doesn't care for overclocking then you can definitely get away with the 4460. that's what separates the two. the feature sets. the K parts are made for overclocking, which will give you extra performance. but realistically, if you're on a budget the regular i5's will be just as fine.

GPUs spend most of their time idling, so power consumption isn't really a argument unless its crazy high like 500+.

4460 i5 + 390 would be neat.
I'd still go for a Fury card though.

he wanted to have a graphics less then 400, the fury is way overpriced that :/

Nothing wrong with going with an older i5 like the 4460 or the 4690k. Skylake will be more expensive and its usually 10 percent better in some games and even in others with the i5-4690k which i imagine are less cpu intensive. Still do some research on benchmarks and ask him if he would be willing to drop an extra 100ish for 10 percent more performanceish. As for gpu the 390 will consume more power you can calculate your costs based on his kwh prices and how many hours per day the comp will be used. If he does consider the 390 i would just say get the 290x if you can get it cheaper or possibly a cheap r9 290 for 240 dollars on newegg assuming you live in the states(if you don't disregard that). The 390x is a refreshed 290x. The gtx 970 consumes less power but the third party coolers for the amd cards are great. As long as his case has decent air flow cooling he won't need to worry about heat at all. If he does decide to go 970 its still a great card that holds up nicely.
http://www.rapidtables.com/calc/electric/energy-consumption-calculator.htm
You can use that site to see your energy costs based on your theoretical maximum power consumption as a worst case scenario.

Any i5 at the end of the day, if overclocking - 'k' cpu + good mb (= more $$$ + good cooler) or vanilla i5 (eg. 4460) + average motherboard (eg h97).

Skylake would be nice but depends on the budget.

I assume the primary use case is gaming so the 'cheap i5 + best gpu one can afford' model applies.

great reply gonna check that website for my comp power usage to..
I decided to reccomend him a i5 4460, its not the best i5 however its suitable for the price

I gave him a look at the MSI H97 GAMING 3 ATX MOBO, however i heard it doesnt come with wifi, so i think he needs to buy a wifi card?

it should be suitable for most games, games are starting to take advantage of more cores but for the vast majority 4 is all you need. The performance difference is not large enough to justify an i 7 or a new skylake imo. It should be able to handle the 970 or 390. Is he planning to keep this computer for a long time? Also yes unless he is able to run an ethernet cable to his router he needs a wifi card. http://www.rapidtables.com/calc/electric/energy-cost-calculator.htm

that one actually allows you to input the cents you pay and it gives you a dollar amount
glad you found it useful and hope that he ends up enjoying his computer!

Something to think about, I just picked up a used 980 for $400 on the local Craigslist. Might be worth a look if used is OK.