Is the £840 budget including the PSU price or without it? If it is without the PSU price I suggest this http://uk.pcpartpicker.com/user/Killerfrenzy96/saved/23Va. With the 750W Psu he could SLI 760's if he wanted and have breathing room. Game's will start using more than 4 core's most likely. So the 8350 will be a little future proof.
Are there any reason for going with the amd side instead of intel side? from what i've could pull out from my research an overclocked intel cpu beats the living crap out of a overclocked amd cpu, and i'm more than likely gonna overclock at some point
The 8350 is still a great CPU, I haven't seen it compared to any Haswell chips, but Haswell didnt make any major performance increases. AMD messed up on Bulldozer, so near everyone jumped on the Intel hype train.