176157 - Arctic Cooling Freezer 7 Pro rev 2 Socket 775, 1156, 1155, 1366, AM2, AM3 Heatpipe CPU Cooler
229934 - Arctic Power Pro 750W Modular 14cm Fan PSU - 4x PCI-E 8x SATA
145450 - Samsung SH-S223 22x DVD±RW DL & RAM SATA Optical Drive - OEM Black
250400 - Asus HD 6950 2GB GDDR5 Dual DVI HDMI Dual DP Out Graphics card
Total £583.15 from ebuyer
Maybe you want to stretch a little futher and get an SLI/xfire board. I wouldn't cheap out on the PSU, CPU can be upgraded, but from a gaming standpoint clocks are better than cores (at least with >=3 cores). GPU will impact much more than CPU. For encoding an SSD would be nice, but seriously capacity is a real factor with big HD files so for your budget better to RAID a couple TB drives.
Everything is of course a matter of opinion. But I think this wouldn't disappoint you too much at all.
gigabyte make solid mobos, I prefer long life as I don't upgrade often.
For your stated priority being gaming first only the CPU's with the highest clocks will make any difference at all. the x4 @3.6GHz is the only one that would have an appreciable difference.
For encoding the number of cores are important, That is why I put forward the triple core. It is sort of best of both worlds, cheap, fast, and a few good cores. Also you can often ~%50-60 of the time unlock the fourth core.
In fact I didn't check if the gigabyte board has that feature in the BIOS. You should check it out because potentially you could get a free core, and if not you still have a really quite fast CPU if it fails.
Anyway, if you want my advice go for the fastest clock speed that keeps it in your budget.
P.S. for attention of Mosox, Your build has half the ram, which could hit encoding capabilities, a 1/4 the hard disk capacity, at ~1/2 the throughput and a no name brand (he specifically said well known brands only) PSU that is kinda underpowered. All that and it costs more too. The cpu won't give better FPS in games as the clock is slower @ only 3.2GHz, it would help encoding as there is the extra core except that your storage throughput is crap as mentioned before, so my build would slam yours there too.
I am not trying to be mean, its just I really think for his stated priorities and budget its not as good.
What resolution ae you gaming at both above builds are graphics heavy which is great if you have a high res monitor but if you are below 1920 x 1080 you want to spend more on the CPU and less on the GPU.
none of those are benchmarks are games^^, a more accurate representation would be found in "Who's Got Game? Twelve Sub-$200 CPUs Compared" here on toms,
However, looking at the test setup page it appears someone "accidently" simulated the athlon IIx3 455 as a 445 with only a 3.1GHz, so even that article doesn't actually show the real lack of difference that paying double for a cpu would make.
And you don't take into account that the 4th core could very easily be unlocked with the click of a button.
Hey guys thanks for all your replies but since this post i have built a gaming pc to my specs, however i took in to consideration americanbrian's advice and did go for a more reasonably priced cpu (see my specs below). However i had to cut back on some things and decided to go with 4gb ram instead of the 8gb to save money and tbh its all i need. Im very happy with the parts i chose and would like to thank everyone who posted for there advice.