I just spent best part of £500 on a ROG board, an i5 4670K and corsair vengeance 2133mhz memory. Performance gain over FX6300 with 990FX sabertooth and 1600mhz DDR3 = nil in games. Waste of money even though all the benchmarks I did on HWbot will say otherwise (except for Firestrike Extreme) because Skyrim played worst at the same graphics settings.
The reason is because I only have 1gb graphics memory and the Intel board runs PCI express x8 when crossfiring my HD 6870's thus causing more choppyness when needing to use the system memory. 990FX chipset makes both slots x16 so not so bad and really smooth at Ultra settings with 2x AA at 720p resolution.
Switching back to a single card making the intel setup x16 again solved the problem and I now have identical performance with one card to what I had crossfired, (I tried more AA and higher res but it won't have it) even so I'm not happy about having to buy another card to make the other "upgrades" worthwhile when I could have just bought a 7950 3gb card for £180 in the first place. My 4670K i5 cost over £170 where I got a deal on a new delivered FX6300 for £67. The i5 is better (will be with a good card) but nowhere near twice as good making it poor value in my book to the point I'm more of an AMD fanboy than I was before I bought it (but I had to know).
I've had a couple of i3's which were alright until the hyperthreading tied them up (works computers, SAGE, website work lots of stuff open etc) they aren't a patch on the AMD quad (socket FM1 or 2 Athlon type APU) I use now.
On a budget the FX6300 is the sweetest performance price point for games by miles, only drawback I found was they are useless with nvidia cards and only seem to work well with 1600mhz memory at CL9. You can go tighter and faster but will see no gains and have less stability. Mine overclocks to 4.3ghz and will run 24/7 without altering the voltage although I wouldn't go that fast on a cheapo board.
Phenom II quads are good too if you can get a black edition at a decent clock, and if you need to scrape the bottom of the barrel the Athlon II x3 are surprisingly ok but make sure its at least 3ghz before you even overclock. Graphics wise 7850 2gb (£106) if you are going new or 2nd hand 6870 2gb (£60) or a Nvidia GTX 560 ti 2gb (£75) but I wouldn't recommend the 6300 with nvidia.
A cheap setup with a £20 aftermarket cooler a £40 case with fans, a £45 branded PSU with 500w and 36amps or more on the 12volt rail will see you through a winter. I rate those seagate momentus hybrid drives as well. I built a cheapo system 4 years ago and have been upgrading ever since, my rig is like Triggers broom! Once you get into it it never ends and you will find yourself writing in forums like this to pass the time on a cold windy night when you've got a lot of answers and are bored of playing games.