I'm currently running on a core i5-4460 CPU @ 3.20GHz on a 1150 LGA socket (Haswell). I need to upgrade to an i7 but I'm unsure on what one to go for, it needs to be faster for compiling code (using the machine for software development) - I'm aware a lot is handled by the SSD, thus I'll be installing 2 in raid 0, but the user has specifically requested an i7. Budget of between £200 and £350. Also, suggestions of trusted supplier would be appreciated (I'm in the UK).
Given that compiling is a thread-heavy job, your user is best off with the i7 that most cheaply gets them the most threads. Given that all i7 CPUs on the 1150 socket feature 8 threads, that means simply getting them the cheapest i7 you can put in that socket, which would likely be the Intel Core i7-4770S or Intel Core i7-4790.
As an aside, Xeon processors are extremely similar to i7 CPUs and fit on this socket. In addition, they support ECC RAM, which is a feature many compiling rigs benefit from due to the high memory usage and long compile times they can undergo. In addition, some Xeons, like the Intel Xeon E3-1275 V3, currently offer higher performance and lower cost than some of those i7s previously mentioned, and would thus be a better fit. Keep in mind to utilize the ECC feature of Xeon processors, the motherboard and RAM must also support ECC.
Amazon.co.uk had the lowest prices I could find on these processors.