I've went from a i7-2600k overclocked to 4.6 ghz to a 3770k @ 4.4 ghz and now a 4770k at @ 4.2 ghz because of heat with same H100i cooler. Honestly the 2600k is a beastly processor that can OC very well and keep up with the 3770k no doubt. 4770k kind of pulls away but its no sacrifice to gaming...
Paying full price of course its not convenient thats why I mentioned if you can get a good deal on it. I recently got a 380x for alot less than $220 and I am sure you can find more like that if you look around as well as a GTX 970 in a really good price range way under the price of a new R9 390.
Best bang for the back which those requierements would definetely fall on the GTX 750 ti FTW card which you can get for a pretty good price used or a GTX 950.
The R9 380x is actually a little bit faster than a GTX 770 which is a pretty good performance gap from a GTX 760 if you get a good deal on it. If he can go for a GTX 970 even though its a little pricier I would recommend that more, you can pick one up for a really good price in mint conditions...
I would go with the GTX 760, the extra 2GB VRAM in that range of card ain't really a big difference but its nice to have. The 680 is definetely too old and those reference cards do get pretty hot so I doubt it has much more life in it and the GTX 750 ti just doesn't have the power. That 760...
There are some great deals on GTX 970's here on the forum, has great performance and low power consumption which is perfect for your setup in my opinion, haven't needed more than a 970 since I only run a 60hz monitor.
With your budget you can definetely find a decent GTX 980 around there, I got a reference design for $340USD shipped which is a little under $500CAN a couple weeks ago and it does marvels with Dying light.
Definitely should back off the GPU overclock a little. 500 watts should be enough but if you want to push everything to the limits you should definitely get atleast a 600 watt PSU.
I would recommend a kit of 32GB Corsair Vengeance Pro RAM, great price and awesome performance. I have the same kit myself.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820233606&cm_re=COrsair_PRO_32GB-_-20-233-606-_-Product
I agree with Quartz-1, most people now a days don't upgrade there old pc's as they are good enough for normal tasks. The market is with graphic designers, video editors, gamers, etc.
I would suggest something like a Fractal Define S which is a great case for $60dlls or a NZXT S340 for $75dlls. Case fans well thats more on personal taste and build color but Corsair AF and SP fans are great and those colored rings have always been my favorite.
Arctic Silver 5 ran around 3-4 degrees hotter than Noctua NT-H1 with a Noctua NH-D14 cooler, ran out and had to use MX-4, it gave me the exact same temps as the NT-H1. Never going back to using AS5 now. Heard Coollaboratory Liquid Pro was pretty decent, not for me though.
It's definitely not optimal, you should flip it around to get better temps. Shouldn't cause any trouble if your not overclocking it, Hyper 212 EVO is a pretty decent cooler.
Yes, I payed an extra premium to overclock my i7-4770k, but the temperatures I was getting @4.4ghz with my H100i w/4 fans were pretty high even after fine tuning the voltage, so I just didn't feel like it was worth the difference in my applications plus the extra noise when it ramps up OC'd. I...
You can get away with the automatic voltage if it is not running too hot, to properly test the max temps that you could download Prime95 to stress the CPU and RealTempGT or HWMonitor to check the temperatures, run tests and see how hot it is running. If you want to go more deep into optimizing...