It is without a doubt remarkable that Intel has broken its tradition by releasing an overclockable Core i3 processor, in addition to the K-models in the more expensive i5 and i7 series. This directly makes it the cheapest CPU from Intel with that feature, which means that overclockers with a smaller budget can now also go for Intel.
For a dual core processor the Core i3 7350K performs well, even out of the box, however its performance is downright impressive with a relatively simple overclock to 5 GHz. This is especially true for programs that are not well-optimized for multiple cores. Two highly-clocked cores are more useful for such applications than four cores with a lower speed.
However, more and more software, including games, is becoming compatible with four or even more cores. For now, the most important competition comes from Intel themselves: the i5 7400 is just as expensive and clocked lower, however it does feature twice the cores. In tasks such as transcoding and rendering the Core i5 is much faster, even when the Core i3 is overclocked.
There already are Core i3 processors with only marginally lower clock speeds for about 125 pounds. In our opinion, the extra premium you pay, just to be able to overclock, is not worth it. Being able to increase the clock frequency is definitely a good point, however it's not a secret spell that makes multi-threaded programs benefit less from CPUs with more core. It feels like you really pay way too much for the Core i3 7350K, especially if you take into consideration that Intel has released the Pentium G4560, a comparable dual core processor with HyperThreading running at 3.5 GHz, for less than 60 pounds.
If you like overclocking, or if you're specially looking for a CPU that is capable of performing single-threaded tasks really quickly, the i3 7350K is a welcome choice. Regular users should probably opt for a cheaper option or a Core i5 - the i3 kind of falls between two stools.