I'd not bother over clocking.
Is it really needed?
thx.
You don't really need to do overclocking. The i5-4690k is already slightly overclocked at 3.5GHz and this is why you need a z97 motherboard. It just gives you the option in the future if you wan't to try. Usually the motherboard has some software bundled with it that can auto-overclock.
Again, the motherboard I suggested was just a cheap one I didn't really look at. Ideally you should spend £80-90 and get an SLI one as it gives more options and may have a few extra gaming features. Choose one you like the look of! You tend to get what you pay for with motherboards (ASUS, MSI, Gigabyte).
Although as Brian1996 pointed out... there are a lot of downsides to SLI - heat, power and performance value for money are the usual suspects. It's better to buy a good card rather than 2 mid-ranged ones.