Have been running a Phenom ii x4 955 3.2ghz, GTX 460 1GB, 4GB DDR2 800mhz with Vista for the last 4 years or so. It served me well up until it tried to take on Metro Last Light, so around September '14 I bought a used EVGA 760 SC ACX for £120 inc p+p with 830-860 days warranty left (love their transferable warranties :D ) which done the job. Then I tried running Transformers Fall of Cybertron and was coming across alot of stutter which lead me to discover that the cpu was hitting a constant 100% on all 4 cores. And when your pc is struggling to run a Transformers game you know it's time for an upgrade.
CPU: So first off, bye bye AMD. If I knew then what I know now I'd probably still be sitting pretty with a 2500k or something. And still in another 4 years I may look back to now and think I should have gone for something different, only time will tell. So buying new it had to be the 4690k but I took a gamble and put down a bit more wonga for the 4790k, it may pay off it may not but looking to the future, developers may start using multi threading more and more especially since the consoles now use 8 threads and since AMD can't keep up on single core I can see them encouraging developers to make use of extra threads, also I think DX12 is supposed to help spread the load.
GPU: Sticking with the 760 for the time being, the new system has doubled the frame rates I was getting previously with it which surprised me. Waiting for the Radeon 3xx series to see how that shakes up the market and see if it's worth investing in a new gpu or not.
RAM: Ram doesn't really effect performance that much so mainly just went with vengeance pro for the slick style. 1866mhz cl9 8GB in dual channel, what more do you need? Although I was thinking of going air cooling initially and the Cryorig R1 ultimate which would have been my choice wouldn't fit in with that ram height ( I believe) although the R1 universal may have.
Motherboard: Spent a bit of time umming and arring over this, I wanted a board with sli capability just so I had options in the future, I'd had 2 Gigabyte motherboards die on me in the past so from personal experience decided I wasn't going to go with them which left me MSI, Asrock and Asus as my top picks. Initially I was going to go with an MSI Z87 G45 for about £80 but they completely disappeared off the market and the few places that still stocked them upped the prices so much they ended up costing either just as much or more as the Z97 G45. In the end I couldn't make my mind up so just threw my hands in the air and went with the low end of the Asus ROG series (yolo).
CPU cooler: I damn near tore my hair out over this, trawling the review sites, videos and forums for information about performance, noise and cost. I'd pretty much made my mind up that I wanted to try an AIO cooler having never used one in the past. I know there are air coolers out there that perform just as well and are generally quieter but its just a pain in the butt cleaning those fins when they get dusty, having to remove the whole heat sink and reapply TIM. With an AIO you just need to stick the hoover up to the rad and you're sorted. Hoover will probably work just aswell on the thinner heat sinks like an evo 212 but on the thicker ones you'll just pick up the dust around the outside. I had a Tt Max Orb previously and a hoover would get the worst off but it still needed a jab with a cotton bud to get into the hard to reach areas. I actually wanted to go with a Cooler Master Nepton 240m, its performance to noise to cost ratio seems to be the best on the market. But I also had decided to go with an NZXT H440 and it appears that 240+ rads can't perform their best in it due to the restricted airflow which means a worse cost:performance ratio. So it came down to the usual suspects, H80i, Kraken X41, Nepton 140XL (and the 120XL although at the time I couldn't find any decent information on it in English). It was a very tight race but I like that the Kraken only used 1 fan which made it less intrusive than other coolers like the H80i which uses 2 whilst maintaining excellent performance and should also produce less noise. Which is another thing I want to mention, I really don't think AIO are as noisy as they're made out to be. At 100% output yes its unbearable but the noise drops alot when you put them down to about 50% (may vary depending on model) and I can drop it even further to 25% which is what i prefer to have it at. I think most of the noise now comes from my GPU and I can hear the hard disk when thats working. Also the performance difference between 25% and 100% was only 5 degrees celcius after running a stress test using OCCT.
Case: It came down to the NZXT H440 and the Corsair 450D. The 450D would get better cooling due to not having its fans covered up and would allow larger radiators to perform optimally but I went for the sleek style of the H440 and hopefully slightly less noise if the sound insulation actually works. These cases really set a standard of quality that all cases should be built to.
PSU: Can't say I know alot about power supplies. I just look up multiple reviews and trust their judgement. The Supernova G2 received great reviews. Fully modular so no excess cables, 750W should be good enough for a couple cards in Sli if I get round to getting a new card or two and the awesome 10 year warranty from EVGA can't be argued with.
Storage: Never used an SSD before but it is nice having your system boot up in 10 seconds (almost seems to take longer for it to shutdown). Samsung appear to be by far the most popular choice so I sided with the masses, was a bit hesitant about the 840 series due to the recent slowdown problems they had but the 850 series just came out so figured I wouldn't worry about it. Just got a cheap 500GB hdd because budget.