i5 with better gpu or i7 with lower gpu

For editting and redering go with the I7 because the i7's have hyperthreading. the extra preformance of youre gpu doesnt make that much of a difference in editing. But for gaming the I5 option is way way better.

Get the i7, you will need the hyper threading with in video rendering and a 750 ti for casual gaming

Do you need windows in that £800?

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i7-4770K 3.5GHz Quad-Core Processor (£236.34 @ Aria PC)
CPU Cooler: RAIJINTEK THEMIS 65.7 CFM Sleeve Bearing CPU Cooler (£19.99 @ Amazon UK)
Motherboard: MSI Z97S SLI Krait Edition ATX LGA1150 Motherboard (£88.76 @ Scan.co.uk)
Memory: Mushkin Blackline 16GB (2 x 8GB) DDR3-1600 Memory (£97.55 @ CCL Computers)
Storage: Crucial BX100 250GB 2.5" Solid State Drive (£73.95 @ Amazon UK)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£42.97 @ CCL Computers)
Video Card: XFX Radeon R9 270 2GB Double Dissipation Video Card (£110.72 @ Scan.co.uk)
Case: Corsair 300R ATX Mid Tower Case (£58.79 @ Aria PC)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply (£48.98 @ Novatech)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer (£10.19 @ Aria PC)
Total: £788.24
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-11 09:22 GMT+0000

If you need windows in budget get 1x8gb ram instead for now.

An i7 is needed if video editing, an SSD is also a must. The r9 270 is a bit faster than the 750ti but only £10 more. The 4770k can be overclocked to 4790k speeds but is £20 cheaper

Dude get the i5 and 960... Best choice there!

Go with the I7 and a R9 270.

If at a later date you need more gaming power, you can get a second 270 for crossfire. It's more expensive to upgrade your CPU from an I5 to an I7 (at a later date) than it is to add another 270 to your build.

If you do go this route, you may need to ammend what PSU you get and make sure your case can take the extra GPU.

Yeah if crossfire is on the cards then an extra £10 on the PSU now makes a ton of sense:

http://www.dabs.com/products/xfx-650w-80--bronze-certified-single-rail-75R9.html?utm_source=awin&utm_medium=affiliates&utm_content=AW00&awc=3044_1426067377_139f0fb27f078109999fd1521177481f&utm_source=awin&utm_medium=affiliates&utm_content=AW00

This should have plenty enough juice for crossfired 270s later on.

Go the i7...and increase your budget - don't muck around with 2013/14 gen GPU's - just get a GTX 970 like the MSI Gaming 4G and be done be with it.

Also, build your system with an SSD drive as the primary - you don't need WD Black's or Blues nonsense...technology is well past that. Sandisk Extreme II 120 or 256GB SSD (or Samsun EVO SSD) and WD Green or a 2 TB Seagate Barracuda will be fine for storage.

RAM...Kingston Hyper X or Beast 1833 is fine...and cheap..Rip Jaws will also do the trick.

Stick with quality, don't buy crap... if you want it, you can scrape up the extra 100 pound

Don't worry about planning crossfire or SLI . the 970 will be ample for your needs for a while to come...in fact by the time you consider it, it'll be 3 years later

Mobo...MSI Gaming 3 or 5 with a Z97 or 99 chipset will be fine - good price point too.

PSU...don't skimp...look at the tier list...just be mindful that you only need a tier 1 or even a tier 2 if you're going to overclock or have a heavy wattage system...which this wont be. 450W to 550W PSU will be more than ample.

Case...up to you...no silver bullet...all have pros and cons...google them, find one you like the look of and run with it. will cost you all of 30 pound to replace the stock fans with Corsair SP fans or other silent varieties. no case is dust proof so ignore the advertising that says otherwise.

CPU cooling - if your not going to overclock - EVO 212 will be fine, even at stock high load. EVO wont handle any overclock where you tweak the voltage up though - you'll need a Noctua D14 or 15 for a medium to high OC, an X61 will be fine for a high OC. If you want to maintain a high to ultra, look at custom cooling - there's other brands of course...but the ones I listed above give best trade off for noise/value/temp (though I'm sure others will disagree)

not to be negative, but do you own research, look at the reviews...everyone on here is an expert and they'll spruik their own build and thoughts as the best...hell, I basically just told you to build the same system as me but on a smaller budget. But, I sit here typing this next to my dead silent system and say "hey, I have an awesome system I built myself and it works freekin well, and i'll share that!"

Are these prebuilt machines? (aka assembled by someone other than you)

yes it is...but worth it. Can you wait a week or two to scrape up the extra cash?

The i7 build is more suited to your needs, and overclockers are a very reputable website.

Try and look on PCPartPicker and choose a mix of sites; you may save some money this way.

So how did you go?

Good choice! as i recommend to you in my earlier post, hyper threading will come handy in video encoding. You can overclock r9 280 to get near 280x performance.

http://www.bit-tech.net/hardware/2014/09/03/intel-core-i7-5930k-and-core-i7-5820k-revie/4

If you don't want to overclock and still want hyper threading is there also the xeon,
http://uk.pcpartpicker.com/part/intel-cpu-bx80646e31231v3
no igp,but cheaper.

Do overclockers uk offer xeons in their custom builds?

Luco makes a very good point here. The Xeon E3-1231V3 costs between the price of an i5-4690k and an i7-4790 but it is actually the same as an i7-4790, just without onboard graphics which you don't need anyways.

This way you can afford an R9 290 in your build and maybe even a GTX 970.

It was vic's point, I was just asking if it's even possible given that OP isn't building it himself